Articles having retained strength

ABSTRACT

One or more aspects of the disclosure pertain to an article including a film disposed on a glass substrate, which may be strengthened, where the interface between the film and the glass substrate is modified, such that the article retains its average flexural strength, and the film retains key functional properties for its application. Some key functional properties of the film include optical, electrical and/or mechanical properties. The bridging of a crack from one of the film or the glass substrate into the other of the film or the glass substrate can be prevented by inserting a crack mitigating layer between the glass substrate and the film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application that claims the benefitof priority under 35 U.S.C. § 120 of U.S. patent application Ser. No.16/597,296, filed on Oct. 9, 2019, which is a divisional applicationthat claims the benefit of priority under 35 U.S.C. § 121 of U.S. patentapplication Ser. No. 14/052,055, filed on Oct. 11, 2013, now U.S. Pat.No. 10,487,009, which claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application No. 61/820,395, filed on May 7,2013, and U.S. Provisional Application No. 61/712,908, filed on Oct. 12,2012, the contents of which are relied upon and incorporated herein byreference in their entireties.

BACKGROUND

This disclosure relates to articles including a glass substrate that hasa film disposed on its surface, and a modified interface between thefilm and the glass substrate such that the glass substrate and/or thearticle substantially retains its average flexural strength, and thefilm retains key properties for its application.

Articles including a glass substrate, which may be strengthened orstrong as described herein, have found wide usage recently as aprotective cover glass for displays, especially in touch-screenapplications, and there is a potential for its use in many otherapplications, such as automotive or architectural windows and glass forphotovoltaic systems. In many of these applications it can beadvantageous to apply a film to the glass substrates. Exemplary filmsinclude indium-tin-oxide (“ITO”) or other transparent conductive oxides(e.g., aluminum and gallium doped zinc oxides and fluorine doped tinoxide), hard films of various kinds (e.g., diamond-like carbon, Al₂O₃,AlN, AlO_(x)N_(y), Si₃N₄, SiO_(x)N_(y), SiAl_(x)O_(y)N_(z) TiN, TiC), IRor UV reflecting layers, conducting or semiconducting layers,electronics layers, thin-film-transistor layers, or anti-reflection(“AR”) films (e.g., SiO₂, Nb₂O₅ and TiO₂ layered structures). In manyinstances these films must necessarily be hard and brittle, or otherwisetheir other functional properties (e.g., mechanical, durability,electrical conductivity, optical properties) will be degraded. In mostcases these films are thin films, that is, they generally have athickness in the range of 0.005 μm to 10 μm (e.g., 5 nm to 10,000 nm).

When a film, as defined herein, is applied to a surface of a glasssubstrate, which may be strengthened or characterized as strong, theaverage flexural strength of the glass substrate may be reduced, forexample, when evaluated using ball-drop or ring-on-ring strengthtesting. This behavior has been measured to be independent oftemperature effects (i.e., the behavior is not caused by significant ormeasureable relaxation of surface compressive stress in the strengthenedglass substrate due to any heating). The reduction in average flexuralstrength is also apparently independent of any glass surface damage orcorrosion from processing, and is apparently an inherent mechanicalattribute of the article, even when thin films having a thickness in therange from about 20 nm to about 200 nm are utilized in the article. Inview of this new understanding, there is a need to prevent films fromreducing the average flexural strength of glass substrates and articlesincluding the same.

SUMMARY

A first aspect of this disclosure pertains to articles that can beutilized in touch-sensing devices, information display devices and othersuch devices. The articles include a film disposed on a glass substrate,where the interface between the film and the glass substrate ismodified, such that the article retains the average flexural surfacestrength of a similar or same glass substrate without the film, and thefilm retains key functional properties (e.g., optical, electrical andmechanical properties) for its application. In one or more embodiments,the interfacial properties between the film and the glass substrate aremodified to prevent a crack from bridging from one of the film or theglass substrate into the other of the film or the glass substrate.

In one or more embodiments, the articles include a crack mitigatinglayer disposed between the film and the glass substrate, which preventscracks originating in one of the film and the glass substrate frombridging into the other of the film and the glass substrate. In one ormore specific embodiments, the crack mitigating layer increases theaverage flexural strength of the article, when compared to articles thatdo not include a crack mitigating layer. In one or more alternativeembodiments, the crack mitigating layer increases the averagestrain-to-failure of the article, when compared to an article thatincludes the glass substrate and film but does not include a crackmitigating layer. In other words, the article including a crackmitigating layer exhibits a greater average strain-to-failure thanarticles with the glass substrate and film but without a crackmitigating layer.

An article according to one or more embodiments has a total reflectivityof 6.0% or less over the visible wavelength range from about 450 nm toabout 650 nm. The article may further exhibit functional properties,such as optical properties, electrical properties and mechanicalproperties, which are improved over articles that include the glasssubstrate and film but do not include a crack mitigating layer. In oneor more embodiments, the article may exhibit improved optical propertiesand electrical properties over articles with the glass substrate andfilm but without a crack mitigating layer. In a more specificembodiment, the article may exhibit improved optical properties andmechanical properties over articles with the glass substrate and filmbut without a crack mitigating layer. In an even more specificembodiment, the article may exhibit improved electrical properties andmechanical properties over articles with the glass substrate and filmbut without a crack mitigating layer. The article may exhibit improvedelectrical properties, optical properties and mechanical properties overarticles with the glass substrate and film but without a crackmitigating layer.

Articles in accordance with one or more embodiments may exhibit greateraverage flexural strength and lower average reflectance over awavelength range from 450-650 nm than articles that include a glasssubstrate and film but do not include a crack mitigating layer.

The glass substrate utilized in one or more embodiments of the articlemay be strengthened or strong, as described herein. In one or moreembodiments, the glass substrate may be chemically strengthened and mayhave a surface compressive stress greater than about 500 MPa and acompressive depth-of-layer greater than about 15 μm. The glass substratemay have a toughness that is greater than the toughness of the interfacebetween the glass substrate and the film. For example, the crackmitigating layer may form a low-adhesion layer or interface between theglass substrate and the film that has a fracture toughness less thanabout 0.5 times or less than about 0.25 times the toughness of the glasssubstrate and/or the toughness of the film. In one or more embodiments,the glass substrate has an average strain-to-failure that is greaterthan about 0.5%, 0.7%, 1.0%, 1.5% or 2%.

The glass substrate of one or more embodiments has a refractive indexthat is less than the refractive index of the crack mitigating layer andthe film. In one or more specific embodiments, the film may have arefractive index that is greater than the refractive index of the crackmitigating layer. In such embodiments, the refractive index of the crackmitigating layer is between the refractive indices of the film and theglass substrate.

The film according to one or more embodiments may exhibit a modulus ofabout 25 GPa or more and/or a hardness of about 1.75 GPa or more. Thefilm may have a fracture toughness of less than about 10 MPa·m^(1/2). Inone or more embodiments, the film has an average strain-to-failure thatis less than the average strain-to-failure of the crack mitigating layerand the glass substrate. The film may include one or more layers such astransparent conductive oxide layers, IR reflecting layers, UV reflectinglayers, conducting layers, semiconducting layers, electronics layers,thin film transistor layers, EMI shielding layers, anti-reflectionlayers, anti-glare layers, dirt-resistant layers, self-cleaning layers,scratch-resistant layers, barrier layers, passivation layers, hermeticlayers, diffusion-blocking layers, fingerprint-resistant layers andcombinations thereof. Exemplary transparent conductive oxide layers mayinclude indium-tin-oxide.

In one or more embodiments, the crack mitigating layer may have acritical strain energy release rate (G_(IC)=K_(IC) ²/E) that is greaterthan the critical strain energy release rate (G_(IC)=K_(IC) ²/E) of thefilm. In specific embodiments, the crack mitigating layer has a criticalstrain energy release rate of 0.1 kJ/m² or greater, while the film has acritical strain energy release rate of less than 0.1 kJ/m². The crackmitigating layer may have an average strain-to-failure that is greaterthan the average strain-to-failure of the film. The averagestrain-to-failure of the film may be less than the averagestrain-to-failure of the glass substrate.

In one or more embodiments, the crack mitigating layer may exhibit ayield stress of less than about 500 MPa and/or a modulus of about 50 GPaor less. The crack mitigating layer may have a fracture toughness of 1MPa·m^(1/2) or greater. The crack mitigating layer may include porousoxides, porous nitrides, porous carbides, porous semi-conductors, poroushybrid organic-inorganic materials, porous or nonporous polymericmaterials or combinations thereof. In a specific embodiment, the crackmitigating layer comprises polyimide.

In one or more specific embodiments, the glass substrate has an averageflexural strength that is maintained when the film is disposed on thefirst major surface and the crack mitigating layer is disposed betweenthe glass substrate and the film. In one or more embodiments, the crackmitigating layer may include polyimide and, in such embodiments, thefilm has an electrical conductivity that is retained or substantiallyretained when the film, the crack mitigating film and glass substrateare combined.

The articles according to one or more embodiments may include anadditional film disposed on the glass substrate, or more specifically onthe film or on the opposite side of the glass substrate from the film.In one or more specific embodiments, the film is disposed between theglass substrate and the additional film. The additional film may includea protective layer, an adhesive layer, a planarizing layer, ananti-splintering layer, an optical bonding layer, a display layer, apolarizing layer, a light-absorbing layer, and/or combinations thereof.

A second aspect of this disclosure pertains to a touch sensor devicethat includes a glass substrate with opposing major surfaces, a filmdisposed on at least a portion of one of the opposing major surfaces ofthe glass substrate so that coated regions (with the film) and uncoatedregions (without the film) are formed on the glass substrate. In one ormore embodiments, a crack mitigating layer is disposed between the filmand the glass substrate, which prevents cracks originating in one of thefilm or the glass substrate from bridging to the other of the film orthe glass substrate. In such embodiments, the coated regions have acoated total reflectance that differs by about 5% or less from the totalreflectance of the uncoated regions. The glass substrate utilized in thetouch sensor devices may be strengthened or strong.

A third aspect of this disclosure pertains to a method for forming anarticle. One or more embodiments of the method include providing a glasssubstrate having opposing major surfaces, disposing a crack mitigatinglayer on a first major surface, and disposing a film on the crackmitigating layer, such that the crack mitigating layer is disposedbetween the film and the glass substrate. The method according to one ormore embodiments includes controlling the thickness of the crackmitigating layer and/or the film to maintain the average flexuralstrength of the glass substrate and the functional properties of thefilm. The method includes disposing an additional film on the film, suchthat the film is between the glass substrate and the additional film. Inone or more alternative embodiments, the additional film may be disposedon the opposite surface of the glass substrate from the film. Theadditional film may include a protective layer, an adhesive layer, aplanarizing layer, an anti-splintering layer, an optical bonding layer,a display layer, a polarizing layer, a light-absorbing layer, andcombinations thereof. The method may further include strengthening theglass substrate, which may optionally be performed before the crackmitigating layer and/or the film are disposed on the glass substrate.

In another aspect of the disclosure, an article is provided thatincludes a glass substrate having opposing major surfaces and athickness from about 600 μm to about 5 mm, the substrate, the substratebeing chemically strengthened and having a surface compressive stress ofat least 500 MPa and a compressive depth of layer 15 μm or greater. Thearticle also includes a crack mitigating layer disposed on and directlyin contact with the first major surface of the substrate. The crackmitigating layer consists of a polyimide film having a thickness fromabout 0.04 μm to about 0.5 μm and a first critical strain energy releaserate (G_(IC)=K_(IC) ²/E). The article further includes a second filmdisposed on and directly in contact with the crack mitigating layerhaving a thickness from about 0.01 μm to about 0.5 μm and having asecond critical strain energy release rate (G_(IC)=K_(IC) ²/E) that isless than the first critical strain energy release rate. The crackmitigating layer increases the average flexural strength of the article,when compared to an article comprising the glass substrate and thesecond film but not the crack mitigating layer. The crack mitigatinglayer prevents cracks originating in one of the second film or the glasssubstrate from bridging to the other of the second film or the glasssubstrate. Further, the second film is exposed.

In another aspect of the disclosure, an article is provided thatincludes a glass substrate having opposing major surfaces and athickness from about 600 μm to about 5 mm, the substrate beingchemically strengthened and having a first average strain-to-failurethat is greater than about 0.5%, a surface compressive stress of atleast 500 MPa and a compressive depth of layer 15 μm or greater. Thearticle also includes a crack mitigating layer disposed on and directlyin contact with the first major surface of the substrate. The crackmitigating layer consists of a polyimide film having a thickness fromabout 0.04 μm to about 0.5 The article also includes a second filmdisposed on and directly in contact with the crack mitigating layer andhaving a thickness from about 0.01 μm to about 0.5 The crack mitigatinglayer prevents cracks originating in one of the second film or the glasssubstrate from bridging to the other of the second film or the glasssubstrate. Further, the second film is exposed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an article comprising a glass substrate, afilm and a crack mitigating layer, according to one or more embodiments.

FIG. 2 is a schematic diagram of the development of a crack in a filmand its possible bridging modes.

FIG. 3 is an illustration of the theoretical model for the presence of acrack in a film and its possible bridging as a function of elasticmismatch α.

FIG. 4 is a diagram illustrating the energy release ratio G_(d)/G_(p).

FIG. 5 is a graph presenting ring-on-ring load-to-failure performance ofglass substrates or articles according to Examples 1A-1J.

FIG. 6 is a probability plot of ball drop performance of glasssubstrates or articles according to Examples 2A-2D.

FIG. 7 is an illustration of an article according to Example 3A.

FIG. 8 is an illustration of an article according to Example 3B.

FIG. 9 is an illustration of an article according to Example 3C.

FIG. 10 is a modeled optical reflectance spectrum according toComparative Examples 4A and 4B.

FIG. 11 is a modeled optical reflectance spectrum according to Example4C and Example 4D.

FIG. 12 is a modeled optical reflectance spectrum according to Example4E and Comparative Example 4F.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details may beset forth in order to provide a thorough understanding of embodiments ofthe disclosure. However, it will be clear to one skilled in the art whenembodiments of the disclosure may be practiced without some or all ofthese specific details. In other instances, well-known features orprocesses may not be described in detail so as not to unnecessarilyobscure the disclosure. In addition, like or identical referencenumerals may be used to identify common or similar elements.

Referring to FIG. 1, aspects of this disclosure include an article 100including a film 110 and a glass substrate 120 wherein the interfacialproperties between the film 110 and the glass substrate 120 are modifiedsuch that the article substantially retains its average flexuralstrength, and the film retains key functional properties for itsapplication. In one or more embodiments, the article exhibits functionalproperties that are also retained after such modification. Functionalproperties of the film and/or article may include optical properties,electrical properties and/or mechanical properties, such as hardness,modulus, strain-to-failure, abrasion resistance, mechanical durability,coefficient of friction, electrical conductivity, electricalresistivity, electron mobility, electron or hole carrier doping, opticalrefractive index, density, opacity, transparency, reflectivity,absorptivity, transmissivity and the like.

In one or more embodiment, the modification to the film-glass substrateinterface includes preventing one or more cracks from bridging from oneof the film 110 or the glass substrate 120 into the other of the film110 or the glass substrate 120, while preserving other functionalproperties of the film 110 and/or the article. In one or more specificembodiments, as illustrated in FIG. 1, the modification of theinterfacial properties includes disposing a crack mitigating layer 130between the glass substrate 120 and the film 110.

The term “film”, as applied to the film 110 and/or other filmsincorporated into the article 100, includes one or more layers that areformed by any known method in the art, including discrete deposition orcontinuous deposition processes. Such layers may be in direct contactwith one another. The layers may be formed from the same material ormore than one different material. In one or more alternativeembodiments, such layers may have intervening layers of differentmaterials disposed therebetween. In one or more embodiments a film mayinclude one or more contiguous and uninterrupted layers and/or one ormore discontinuous and interrupted layers (i.e., a layer havingdifferent materials formed adjacent to one another). As used herein, theterm “layer” may include a single layer or a plurality of sub-layers.Layer may also include a single-molecule “monolayer”.

As used herein, the term “dispose” includes coating, depositing and/orforming a material onto a surface using any known method in the art. Thedisposed material may constitute a layer or film as defined herein. Thephrase “disposed on” includes the instance of forming a material onto asurface such that the material is in direct contact with the surface andalso includes the instance where the material is formed on a surface,where one or more intervening material(s) is between the disposedmaterial and the surface. The intervening material(s) may constitute alayer or film, as defined herein.

As used herein, the term “average flexural strength” is intended torefer to the flexural strength of a glass-containing material (e.g., anarticle and/or a glass substrate), as tested through methods such asring-on-ring, ball-on-ring, or ball drop testing. The term “average”when used in connection with average flexural strength or any otherproperty is based on the mathematical average of measurements of suchproperty on at least 5 samples, at least 10 samples or at least 15samples or at least 20 samples. Average flexural strength may refer tothe scale parameter of two parameter Weibull statistics of failure loadunder ring-on-ring or ball-on-ring testing. This scale parameter is alsocalled the Weibull characteristic strength, at which a brittlematerial's failure probability is 63.2%. More broadly, average flexuralstrength may also be defined by other tests such as a ball drop test,where the glass surface flexural strength is characterized by a balldrop height that can be tolerated without failure. Glass surfacestrength may also be tested in a device configuration, where anappliance or device containing the glass-containing material (e.g., anarticle and/or a glass substrate) article is dropped in differentorientations that may create a surface flexural stress. Average flexuralstrength may in some cases also incorporate the strength as tested byother methods known in the art, such as 3-point bend or 4-point bendtesting. In some cases, these test methods may be significantlyinfluenced by the edge strength of the article.

In one or more embodiments, the crack mitigating layer 130 prevents oneor more cracks originating in one of the film 110 or the glass substrate120 from bridging into the other of the film 110 or the glass substrate120. In one or more specific embodiments, the crack mitigating layer 130prevents crack bridging from one of the film 110 or the glass substrate120 into the other of the film 110 or the glass substrate 120 by causingan increase in the average strain-to-failure of the film 110. The crackmitigating layer 130 may increase the average strain-to-failure of thefilm 110 by reducing the stress that may be formed in the film 110during formation or application on the glass substrate. In suchembodiments, it is believed that the increase in the averagestrain-to-failure of the film 110 prevents cracks from bridging from oneof the film 110 or the glass substrate 120 into the other of the film110 or the glass substrate 120. In other embodiments, the crackmitigating layer 130 does not change the strain-to-failure of the film110, that is, cracks still form in the film 110 under loading, but thesecracks are prevented from bridging to the glass substrate 120 from thefilm 110 by the crack mitigating layer 130. In these embodiments, thecrack mitigating layer 130 may prevent the cracks in the film 110 frombridging to the glass substrate 120 through crack tip blunting, crackarrest, crack deflection, delamination, or other related mechanisms, aswill be further described below.

As used herein, the terms “bridge”, or “bridging”, refer to crack, flawor defect formation and such crack, flaw or defect's growth in sizeand/or propagation from one material, layer or film into anothermaterial, layer or film. For example, bridging includes the instancewhere a crack that is present in the film 110 propagates into anothermaterial, layer or film (e.g., the glass substrate 120). The terms“bridge” or “bridging” also include the instance where a crack crossesan interface between different materials, different layers and/ordifferent films. The materials, layers and/or films need not be indirect contact with one another for a crack to bridge between suchmaterials, layers and/or films. For example, the crack may bridge from afirst material into a second material, not in direct contact with thefirst material, by bridging through an intermediate material disposedbetween the first and second material. The same scenario may apply tolayers and films and combinations of materials, layers and films. In thearticles described herein, a crack may originate in one of the film 110or the glass substrate 120 and bridge into the other of the film 110 orthe glass substrate 120. As will be described herein, the crackmitigating layer 130 may prevent cracks from bridging between the film110 and the glass substrate 120, regardless of where (i.e., the film 110or the glass substrate 120) the crack originates.

The term “prevent”, when associated with prevention of crack bridging,refers to preventing crack bridging at one or more selected loadlevel(s) (or ranges of loads) or flexural state(s). This does not implythat crack bridging is prevented for all load levels or flexural states.Rather, this generally implies that crack bridging is prevented for aparticular load, stress, or strain level or range that would ordinarilycause crack bridging without the presence of the crack mitigating layer.

The following theoretical fracture mechanics analysis illustrates theways in which cracks may bridge within a article. FIG. 2 is a schematicillustrating the presence of a crack in a film disposed on a glasssubstrate and its possible bridging modes. The numbered elements in FIG.2 are the glass substrate 10, the film 12 on top of a surface(unnumbered) of glass substrate 10, a two-sided deflection 14 into theinterface between glass substrate 10 and film 12, an arrest 16 which isa crack that started to develop in film 12 but did not go completelythrough film 12, a “kinking” 18 which is a crack that developed in thesurface of film 12, but when it reached the surface of the glasssubstrate 10 it did not penetrate into the glass substrate 12, insteadit moved in a lateral direction as indicated in FIG. 2 and thenpenetrates the surface of the glass substrate 10 at another position, apenetration crack 11 that developed in the film 12 and penetrated intothe glass substrate 10, a one-sided deflection 13, and a graph oftension vs. compression 17 in the glass substrate 10 compared to zeroaxis 15. Note that this schematic is not to scale and the glasssubstrate thickness typically extends further past the bottom of thefigure (not shown). As illustrated, upon application of external loading(in such cases, tensile loading is the most detrimental situation), theflaws in the film can be preferentially activated to form cracks priorto the development of cracks in the residually compressed glasssubstrate. In the scenarios illustrated in FIG. 2, with continuedincrease of external loading, the cracks will bridge until theyencounter the glass substrate. When the cracks reach the surface ofsubstrate 10 the possible bridging modes of the crack, when itoriginates in the film are: (a) penetration into the glass substratewithout changing its path as represented by numeral 11; (b) deflectioninto one side along the interface between the film and the glasssubstrate as indicated by numeral 13; (c) deflection into two sidesalong the interface as indicated by numeral 14, (d) first deflectionalong the interface and then kinking into the glass substrate asindicated by numeral 18, or (e) crack arrest as indicated by numeral 16due to microscopic deformation mechanisms, for example, plasticity,nano-scale blunting, or nano-scale deflection at the crack tip. Cracksmay originate in the film and may bridge into the glass substrate. Theabove described bridging modes are also applicable where cracksoriginate in the glass substrate and bridge into the film, for examplewhere pre-existing cracks or flaws in the glass substrate may induce ornucleate cracks or flaws in the film, thus leading to crack growth orpropagation from the glass substrate into the film, resulting in crackbridging.

Crack penetration into the glass substrate and/or film reduces theaverage flexural strength of the article and the glass substrate ascompared to the average flexural strength of the glass substrate alone(i.e., without a film or a crack mitigating layer), while crackdeflection, crack blunting or crack arrest (collectively referred toherein as crack mitigation) is preferable to help retain the averageflexural strength of the article. Crack blunting and crack arrest can bedistinguished from one another. Crack blunting may comprise anincreasing crack tip radius, for example, through plastic deformation oryielding mechanisms. Crack arrest, on the other hand, could comprise anumber of different mechanisms such as, for example, encountering ahighly compressive stress at the crack tip a reduction of the stressintensity factor at the crack tip resulting from the presence of alow-modulus interlayer or a low-modulus-to-high-modulus interfacetransition; nano-scale crack deflection or crack tortuosity, nano-scalecrack deflection or crack tortuosity as in some polycrystalline orcomposite materials, strain hardening at the crack tip and the like.

Without being bound by theory, certain possible crack bridging paths canbe analyzed in the context of linear elastic fracture mechanics. In thefollowing paragraphs, one crack path is used as an example and thefracture mechanics concept is applied to the crack path to analyze theproblem and illustrate the requirements of material parameters to helpretain the average flexural strength performance of the article, for aparticular range of materials properties.

FIG. 3 below shows the illustration of the theoretical model framework.This is a simplified schematic view of the interface region between thefilm 12 and glass substrate 10. The terms μ₁, E₁, ν₁, and μ₂, E₂, ν₂,are shear modulus, Young's modulus, Poisson's ratio of glass substrateand film materials, Γ_(c) ^(Glass) and Γ_(c) ^(IT) are critical energyrelease rate of glass substrate and the interface between substrate andfilm, respectively.

The common parameters to characterize the elastic mismatch between thefilm and the substrate are Dundurs' parameters α and β [1], as definedbelow

$\begin{matrix}{\alpha = \frac{{\overset{\_}{E}}_{1} - {\overset{\_}{E}}_{2}}{{\overset{\_}{E}}_{1} + {\overset{\_}{E}}_{2}}} & (1)\end{matrix}$

where Ē=E/(1−ν²) for plain strain and

$\begin{matrix}{\beta = {\frac{1}{2}\frac{{\mu_{1}\left( {1 - {2v_{2}}} \right)} - {\mu_{2}\left( {1 - {2v_{1}}} \right)}}{{\mu_{1}\left( {1 - v_{2}} \right)} + {\mu_{2}\left( {1 - v_{1}} \right)}}}} & (2)\end{matrix}$

It is worth pointing out that critical energy release rate is closelyrelated with the fracture toughness of the material through therelationship defined as

$\begin{matrix}{\Gamma = {\frac{1 - v^{2}}{E}K_{C}^{2}}} & (3)\end{matrix}$

Under the assumption that there is a pre-existing flaw in the film, upontensile loading the crack will extend vertically down as illustrated inFIG. 3. Right at the interface, the crack tends to deflect along theinterface if

$\begin{matrix}{\frac{G_{d}}{G_{p}} \geq \frac{\Gamma_{c}^{IT}}{\Gamma_{c}^{Glass}}} & (4)\end{matrix}$

and the crack will penetrate into the glass substrate if

$\begin{matrix}{\frac{G_{d}}{G_{p}} \leq \frac{\Gamma_{c}^{IT}}{\Gamma_{c}^{Glass}}} & (5)\end{matrix}$

where G_(d) and G_(p) and are energy release rates between deflectedcrack along the interface and the penetrated crack into the glasssubstrate [1]. On the left hand side of equations (4) and (5), the ratioG_(d)/G_(p) is a strong function of elastic mismatch parameter α andweakly dependent on β; and on the right hand side, the toughness ratioΓ_(c) ^(IT)/Γ_(c) ^(Glass) is a material parameter.

FIG. 4 graphically illustrates the trend of G_(d)/G_(p) as a function ofelastic mismatch α, reproduced from reference for doubly deflectedcracks. (Ming-Yuan, H. and J. W. Hutchinson, Crack deflection at aninterface between dissimilar elastic materials. International Journal ofSolids and Structures, 1989. 25(9): p. 1053-1067.).

It is evident that the ratio G_(d)/G_(p) is strongly dependent on α.Negative α means the film is stiffer than the glass substrate andpositive a means the film is softer than the glass substrate. Thetoughness ratio Γ_(c) ^(IT)/Γ_(c) ^(Glass), which is independent of α isa horizontal line in FIG. 4. If criterion (4) is satisfied, in FIG. 4,at the region above the horizontal line, the crack tends to deflectalong the interface and therefore is beneficial for the retention of asubstrate's average flexural strength. On the other hand, if thecriterion (5) is satisfied, in FIG. 4, at the region below thehorizontal line, the crack tends to penetrate into glass substrateresulting in degradation of the average flexural strength.

With the above concept, in the following, an indium-tin-oxide (ITO) filmis utilized as an illustrative example. For glass substrate, E₁=72 GPa,ν₁=0.22, and K_(1c)=0.7 MPa m^(1/2); for ITO, E₂=99.8 GPa, ν₂=0.25.(Zeng, K., et al., Investigation of mechanical properties of transparentconducting oxide thin films. Thin Solid Films, 2003. 443(1-2): p.60-65.). The interfacial toughness between the ITO film and glasssubstrate can be approximately Γ_(in)=5 J/m², depending on depositionconditions. (Cotterell, B. and Z. Chen, Buckling and cracking of thinfilms on compliant substrates under compression. International Journalof Fracture, 2000. 104(2): p. 169-179.). This will give the elasticmismatch α=−0.17 and Γ_(c) ^(IT)/Γ_(c) ^(Glass)=0.77. These values areplotted in FIG. 4. This fracture analysis predicts that the crackpenetration into the glass substrate for the ITO film leading todegradation of the average flexural strength of the glass. This isbelieved to be one of the potential underlying mechanisms observed withvarious indium-tin-oxide or other transparent conductive oxide filmsthat are disposed on glass substrates, including strengthened or strongglass substrates. As shown in FIG. 4, one way to mitigate thedegradation of the average flexural strength can be to selectappropriate materials to change the elastic mismatch α (choice 1) or toadjust the interfacial toughness (choice 2).

The theoretical analysis outlined above suggests that a crack mitigatinglayer 130 can be used to better retain the article strength.Specifically, the insertion of a crack mitigating layer between a glasssubstrate 120 and a film 110 makes crack mitigation, as defined herein,a more preferred path and thus the article is better able to retain itsstrength.

Glass Substrate

Referring to FIG. 1, the article 100 includes a glass substrate 120,which may be strengthened or strong, as described herein, havingopposing major surfaces 122, 124, a film 110 disposed on a at least oneopposing major surface (122 or 124) and a crack mitigating layer 130disposed between the film 110 and the glass substrate 120. In one ormore alternative embodiments, the crack mitigating layer 130 and thefilm 110 may be disposed on the minor surface(s) of the glass substratein addition to or instead of being disposed on at least one majorsurface (122 or 124). As used herein, the glass substrate 120 may besubstantially planar sheets, although other embodiments may utilize acurved or otherwise shaped or sculpted glass substrate. The glasssubstrate 120 may be substantially clear, transparent and free fromlight scattering. The glass substrate may have a refractive index in therange from about 1.45 to about 1.55. In one or more embodiments, theglass substrate 120 may be strengthened or characterized as strong, aswill be described in greater detail herein. The glass substrate 120 maybe relatively pristine and flaw-free (for example, having a low numberof surface flaws or an average surface flaw size less than about 1micron) before such strengthening. Where strengthened or strong glasssubstrates 120 are utilized, such substrates may be characterized ashaving a high average flexural strength (when compared to glasssubstrates that are not strengthened or strong) or high surfacestrain-to-failure (when compared to glass substrates that are notstrengthened or strong) on one or more major opposing surfaces of suchsubstrates.

Additionally or alternatively, the thickness of the glass substrate 120may vary along one or more of its dimensions for aesthetic and/orfunctional reasons. For example, the edges of the glass substrate 120may be thicker as compared to more central regions of the glasssubstrate 120. The length, width and thickness dimensions of the glasssubstrate 120 may also vary according to the article 100 application oruse.

The glass substrate 120 according to one or more embodiments includes anaverage flexural strength that may be measured before and after theglass substrate 120 is combined with the film 110, crack mitigatinglayer 130 and/or other films or layers. In one or more embodimentsdescribed herein, the article 100 retains its average flexural strengthafter the combination of the glass substrate 120 with the film 110,crack mitigating layer 130 and/or other films, layers or materials, whencompared to the average flexural strength of the glass substrate 120before such combination. In other words, the average flexural strengthof the article 100 is substantially the same before and after the film110, crack mitigating layer 130 and/or other films or layers aredisposed on the glass substrate 120. In one or more embodiments, thearticle 100 has an average flexural strength that is significantlygreater than the average flexural strength of a similar article thatdoes not include the crack mitigating layer 130 (e.g. higher strengththan an article that comprises film 110 and glass substrate 120 indirect contact, without an intervening crack mitigating layer).

In accordance with one or more embodiments, the glass substrate 120 hasan average strain-to-failure that may be measured before and after theglass substrate 120 is combined with the film 110, crack mitigatinglayer 130 and/or other films or layers. The term “averagestrain-to-failure” refers to the strain at which cracks propagatewithout application of additional load, typically leading tocatastrophic failure in a given material, layer or film and, perhapseven bridge into another material, layer of film, as defined herein.Average strain-to-failure may be measured using, for example,ball-on-ring testing. Without being bound by theory, the averagestrain-to-failure may be directly correlated to the average flexuralstrength using appropriate mathematical conversions. In specificembodiments, the glass substrate 120, which may be strengthened orstrong as described herein, has an average strain-to-failure that is0.5% or greater, 0.6% or greater, 0.7% or greater, 0.8% or greater, 0.9%or greater, 1% or greater, 1.1% or greater, 1.2% or greater, 1.3% orgreater, 1.4% or greater 1.5% or greater or even 2% or greater. Inspecific embodiments, the glass substrate has an averagestrain-to-failure of 1.2%, 1.4%, 1.6%, 1.8%, 2.2%, 2.4%, 2.6%, 2.8% or3% or greater. The average strain-to-failure of the film 110 may be lessthan the average strain-to-failure of the glass substrate 120 and/or theaverage strain-to-failure of the crack mitigating layer 130. Withoutbeing bound by theory, it is believed that the average strain-to-failureof a glass substrate or any other material is dependent on the surfacequality of such material. With respect to glass substrates, the averagestrain-to-failure of a specific glass substrate is dependent on theconditions of ion exchange or strengthening process utilized in additionto or instead of the surface quality of the glass substrate.

In one or more embodiments, the glass substrate 120 retains its averagestrain-to-failure after combination with the film 110, crack mitigatinglayer 130 and/or other films or layers. In other words, the averagestrain-to-failure of the glass substrate 120 is substantially the samebefore and after the film 110, crack mitigating layer 130 and/or otherfilms or layers are disposed on the glass substrate 120.

The glass substrate 120 may be provided using a variety of differentprocesses. For instance, example glass substrate forming methods includefloat glass processes and down-draw processes such as fusion draw andslot draw.

In the float glass process, a glass substrate that may be characterizedby smooth surfaces and uniform thickness is made by floating moltenglass on a bed of molten metal, typically tin. In an example process,molten glass that is fed onto the surface of the molten tin bed forms afloating glass ribbon. As the glass ribbon flows along the tin bath, thetemperature is gradually decreased until the glass ribbon solidifiesinto a solid glass substrate that can be lifted from the tin ontorollers. Once off the bath, the glass substrate can be cooled furtherand annealed to reduce internal stress.

Down-draw processes produce glass substrates having a uniform thicknessthat may possess relatively pristine surfaces. Because the averageflexural strength of the glass substrate is controlled by the amount andsize of surface flaws, a pristine surface that has had minimal contacthas a higher initial strength. When this high strength glass substrateis then further strengthened (e.g., chemically), the resultant strengthcan be higher than that of a glass substrate with a surface that hasbeen lapped and polished. Down-drawn glass substrates may be drawn to athickness of less than about 2 mm. In addition, down drawn glasssubstrates may have a very flat, smooth surface that can be used in itsfinal application without costly grinding and polishing.

The fusion draw process, for example, uses a drawing tank that has achannel for accepting molten glass raw material. The channel has weirsthat are open at the top along the length of the channel on both sidesof the channel. When the channel fills with molten material, the moltenglass overflows the weirs. Due to gravity, the molten glass flows downthe outside surfaces of the drawing tank as two flowing glass films.These outside surfaces of the drawing tank extend down and inwardly sothat they join at an edge below the drawing tank. The two flowing glassfilms join at this edge to fuse and form a single flowing glasssubstrate. The fusion draw method offers the advantage that, because thetwo glass films flowing over the channel fuse together, neither of theoutside surfaces of the resulting glass substrate comes in contact withany part of the apparatus. Thus, the surface properties of the fusiondrawn glass substrate are not affected by such contact.

The slot draw process is distinct from the fusion draw method. In slotdraw processes, the molten raw material glass is provided to a drawingtank. The bottom of the drawing tank has an open slot with a nozzle thatextends the length of the slot. The molten glass flows through theslot/nozzle and is drawn downward as a continuous substrate and into anannealing region.

Once formed, glass substrates may be strengthened to form strengthenedglass substrates. As used herein, the term “strengthened glasssubstrate” may refer to a glass substrate that has been chemicallystrengthened, for example through ion-exchange of larger ions forsmaller ions in the surface of the glass substrate. However, otherstrengthening methods known in the art, such as thermal tempering, maybe utilized to form strengthened glass substrates. As will be described,strengthened glass substrates may include a glass substrate having asurface compressive stress in its surface that aids in the strengthpreservation of the glass substrate. Strong glass substrates are alsowithin the scope of this disclosure and include glass substrates thatmay not have undergone a specific strengthening process, and may nothave a surface compressive stress, but are nevertheless strong. Suchstrong glass substrates articles may be defined as glass sheet articlesor glass substrates having an average strain-to-failure greater thanabout 0.5%, 0.7%, 1%, 1.5%, or even greater than 2%. Such strong glasssubstrates can be made, for example, by protecting the pristine glasssurfaces after melting and forming the glass substrate. An example ofsuch protection occurs in a fusion draw method, where the surfaces ofthe glass films do not come into contact with any part of the apparatusor other surface after forming. The glass substrates formed from afusion draw method derive their strength from their pristine surfacequality. A pristine surface quality can also be achieved through etchingor polishing and subsequent protection of glass substrate surfaces, andother methods known in the art. In one or more embodiments, bothstrengthened glass substrates and the strong glass substrates maycomprise glass sheet articles having an average strain-to-failuregreater than about 0.5%, 0.7%, 1%, 1.5%, or even greater than 2%, forexample when measured using ring-on-ring or ball-on-ring flexuraltesting.

As mentioned above, the glass substrates described herein may bechemically strengthened by an ion exchange process to provide astrengthened glass substrate 120. The glass substrate may also bestrengthened by other methods known in the art, such as thermaltempering. In the ion-exchange process, typically by immersion of theglass substrate into a molten salt bath for a predetermined period oftime, ions at or near the surface(s) of the glass substrate areexchanged for larger metal ions from the salt bath. In one embodiment,the temperature of the molten salt bath is about 350° C. to 450° C. andthe predetermined time period is about two to about eight hours. Theincorporation of the larger ions into the glass substrate strengthensthe glass substrate by creating a compressive stress in a near surfaceregion or in regions at and adjacent to the surface(s) of the glasssubstrate. A corresponding tensile stress is induced within a centralregion or regions at a distance from the surface(s) of the glasssubstrate to balance the compressive stress. Glass substrates utilizingthis strengthening process may be described more specifically aschemically-strengthened glass substrates 120 or ion-exchanged glasssubstrates 120. Glass substrates that are not strengthened may bereferred to herein as non-strengthened glass substrates.

In one example, sodium ions in a strengthened glass substrate 120 arereplaced by potassium ions from the molten bath, such as a potassiumnitrate salt bath, though other alkali metal ions having larger atomicradii, such as rubidium or cesium, can replace smaller alkali metal ionsin the glass. According to particular embodiments, smaller alkali metalions in the glass can be replaced by Ag⁺ ions. Similarly, other alkalimetal salts such as, but not limited to, sulfates, phosphates, halides,and the like may be used in the ion exchange process.

The replacement of smaller ions by larger ions at a temperature belowthat at which the glass network can relax produces a distribution ofions across the surface(s) of the strengthened glass substrate 120 thatresults in a stress profile. The larger volume of the incoming ionproduces a compressive stress (CS) on the surface and tension (centraltension, or CT) in the center of the strengthened glass substrate 120.The compressive stress is related to the central tension by thefollowing relationship:

${CS} = {C{T\left( \frac{t - {2DOL}}{DOL} \right)}}$

where t is the total thickness of the strengthened glass substrate 120and compressive depth of layer (DOL) is the depth of exchange. Depth ofexchange may be described as the depth within the strengthened glasssubstrate 120 (i.e., the distance from a surface of the glass substrateto a central region of the glass substrate), at which ion exchangefacilitated by the ion exchange process takes place.

In one embodiment, a strengthened glass substrate 120 can have a surfacecompressive stress of 300 MPa or greater, e.g., 400 MPa or greater, 450MPa or greater, 500 MPa or greater, 550 MPa or greater, 600 MPa orgreater, 650 MPa or greater, 700 MPa or greater, 750 MPa or greater or800 MPa or greater. The strengthened glass substrate 120 may have acompressive depth of layer 15 μm or greater, 20 μm or greater (e.g., 25μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or greater) and/or a centraltension of 10 MPa or greater, 20 MPa or greater, 30 MPa or greater, 40MPa or greater (e.g., 42 MPa, 45 MPa, or 50 MPa or greater) but lessthan 100 MPa (e.g., 95, 90, 85, 80, 75, 70, 65, 60, 55 MPa or less). Inone or more specific embodiments, the strengthened glass substrate 120has one or more of the following: a surface compressive stress greaterthan 500 MPa, a depth of compressive layer greater than 15 μm, and acentral tension greater than 18 MPa.

Without being bound by theory, it is believed that strengthened glasssubstrates 120 with a surface compressive stress greater than 500 MPaand a compressive depth of layer greater than about 15 μm typically havegreater strain-to-failure than non-strengthened glass substrates (or, inother words, glass substrates that have not been ion exchanged orotherwise strengthened). In some embodiments, the benefits of one ormore embodiments described herein may not be as prominent withnon-strengthened or weakly strengthened types of glass substrates thatdo not meet these levels of surface compressive stress or compressivedepth of layer, because of the presence of handling or common glasssurface damage events in many typical applications. However, asmentioned previously, in other specific applications where the glasssubstrate surfaces can be adequately protected from scratches or surfacedamage (for example by a protective coating or other layers), strongglass substrates with a relatively high strain-to-failure can also becreated through forming and protection of a pristine glass surfacequality, using methods such as the fusion forming method. In thesealternate applications, the benefits of one or more embodimentsdescribed herein can be similarly realized.

Example ion-exchangeable glasses that may be used in the strengthenedglass substrate 120 may include alkali aluminosilicate glasscompositions or alkali aluminoborosilicate glass compositions, thoughother glass compositions are contemplated. As used herein, “ionexchangeable” means that a glass substrate is capable of exchangingcations located at or near the surface of the glass substrate withcations of the same valence that are either larger or smaller in size.One example glass composition comprises SiO₂, B₂O₃ and Na₂O, where(SiO₂+B₂O₃)≥66 mol. %, and Na₂O≥9 mol. %. In an embodiment, the glasssubstrate 120 includes a glass composition with at least 6 wt. %aluminum oxide. In a further embodiment, a glass substrate 120 includesa glass composition with one or more alkaline earth oxides, such that acontent of alkaline earth oxides is at least 5 wt. %. Suitable glasscompositions, in some embodiments, further comprise at least one of K₂O,MgO, and CaO. In a particular embodiment, the glass compositions used inthe glass substrate 120 can comprise 61-75 mol. % SiO₂; 7-15 mol. %Al₂O₃; 0-12 mol. % B₂O₃; 9-21 mol. % Na₂O; 0-4 mol. % K₂O; 0-7 mol. %MgO; and 0-3 mol. % CaO.

A further example glass composition suitable for the glass substrate120, which may optionally be strengthened or strong, comprises: 60-70mol. % SiO₂; 6-14 mol. % Al₂O₃; 0-15 mol. % B₂O₃; 0-15 mol. % Li₂O; 0-20mol. % Na₂O; 0-10 mol. % K₂O; 0-8 mol. % MgO; 0-10 mol. % CaO; 0-5 mol.% ZrO₂; 0-1 mol. % SnO₂; 0-1 mol. % CeO₂; less than 50 ppm As₂O₃; andless than 50 ppm Sb₂O₃; where 12 mol. %≤(Li₂O+Na₂O+K₂O)≤20 mol. % and 0mol. %≤(MgO+CaO)≤10 mol. %.

A still further example glass composition suitable for the glasssubstrate 120, which may optionally be strengthened or strong,comprises: 63.5-66.5 mol. % SiO₂; 8-12 mol. % Al₂O₃; 0-3 mol. % B₂O₃;0-5 mol. % Li₂O; 8-18 mol. % Na₂O; 0-5 mol. % K₂O; 1-7 mol. % MgO; 0-2.5mol. % CaO; 0-3 mol. % ZrO₂; 0.05-0.25 mol. % SnO₂; 0.05-0.5 mol. %CeO₂; less than 50 ppm As₂O₃; and less than 50 ppm Sb₂O₃; where 14 mol.%≤(Li₂O+Na₂O+K₂O)≤18 mol. % and 2 mol. %≤(MgO+CaO)≤7 mol. %.

In a particular embodiment, an alkali aluminosilicate glass compositionsuitable for the glass substrate 120, which may optionally bestrengthened or strong, comprises alumina, at least one alkali metaland, in some embodiments, greater than 50 mol. % SiO₂, in otherembodiments at least 58 mol. % SiO₂, and in still other embodiments atleast 60 mol. % SiO₂, wherein the ratio

${\frac{{{Al}_{2}O_{3}} + {B_{2}O_{3}}}{\sum{modifiers}} > 1},$

where in the ratio the components are expressed in mol. % and themodifiers are alkali metal oxides. This glass composition, in particularembodiments, comprise: 58-72 mol. % SiO₂; 9-17 mol. % Al₂O₃; 2-12 mol. %B₂O₃; 8-16 mol. % Na₂O; and 0-4 mol. % K₂O, wherein the ratio

$\frac{{{Al}_{2}O_{3}} + {B_{2}O_{3}}}{\sum{modifiers}} > 1.$

In still another embodiment, the glass substrate, which may optionallybe strengthened or strong, may include an alkali aluminosilicate glasscomposition comprising: 64-68 mol. % SiO₂; 12-16 mol. % Na₂O; 8-12 mol.% Al₂O₃; 0-3 mol. % B₂O₃; 2-5 mol. % K₂O; 4-6 mol. % MgO; and 0-5 mol. %CaO, wherein: 66 mol. %≤SiO₂+B₂O₃+CaO≤69 mol. %;Na₂O+K₂O+B₂O₃+MgO+CaO+SrO>10 mol. %; 5 mol. %≤MgO+CaO+SrO≤8 mol. %;(Na₂O+B₂O₃)−Al₂O₃≤2 mol. %; 2 mol. %≤Na₂O−Al₂O₃≤6 mol. %; and 4 mol.%≤(Na₂O+K₂O)−Al₂O₃≤10 mol. %.

In some embodiments, the glass substrate 120, which may optionally bestrengthened or strong, may comprise an alkali silicate glasscomposition comprising: 2 mol % or more of Al₂O₃ and/or ZrO₂, or 4 mol %or more of Al₂O₃ and/or ZrO₂.

In some embodiments, the glass substrate used in the glass substrate 120may be batched with 0-2 mol. % of at least one fining agent selectedfrom a group that includes Na₂SO₄, NaCl, NaF, NaBr, K₂SO₄, KCl, KF, KBr,and SnO₂.

The glass substrate 120 according to one or more embodiments can have athickness ranging from about 50 μm to 5 mm. Example glass substrate 120thicknesses range from 100 μm to 500 μm, e.g., 100, 200, 300, 400 or 500μm. Further example glass substrate 120 thicknesses range from 500 μm to1000 μm, e.g., 500, 600, 700, 800, 900 or 1000 μm. The glass substrate120 may have a thickness greater than 1 mm, e.g., about 2, 3, 4, or 5mm. In one or more specific embodiments, the glass substrate 120 mayhave a thickness of 2 mm or less or less than 1 mm. The glass substrate120 may be acid polished or otherwise treated to remove or reduce theeffect of surface flaws.

Film

The article 100 includes a film 110 disposed on a surface of the glasssubstrate 120. The film 110 may be disposed on one or both majorsurfaces 122, 124 of the glass substrate 120. In one or moreembodiments, the film 110 may be disposed on one or more minor surfaces(not shown) of the glass substrate 120 in addition to or instead ofbeing disposed on one or both major surfaces 122, 124. In one or moreembodiments, the film 110 is free of macroscopic scratches or defectsthat are easily visible to the eye.

In one or more embodiments, the film 110 may lower the average flexuralstrength of articles incorporating such a film and glass substrate,through the mechanisms described herein. In one or more embodiments,such mechanisms include instances in which the film 110 may lower theaverage flexural strength of the article because crack(s) developing insuch film bridge into the glass substrate. In other embodiments, themechanisms include instances in which the film may lower the averageflexural strength of the article because cracks developing in the glasssubstrates bridge into the film. The film 110 of one or more embodimentsmay exhibit a strain-to-failure of 2% or less or a strain-to-failurethat is less than the strain to failure of the glass substratesdescribed herein. Films including any of these attributes may becharacterized as brittle.

In accordance with one or more embodiments, the film 110 may have astrain-to-failure (or crack onset strain level) that is lower than thestrain-to-failure of the glass substrate 120. For example, the film 110may have strain-to-failure of about 2% or less, about 1.8% or less,about 1.6% or less, about 1.5% or less, about 1.4% or less, about 1.2%or less, about 1% or less, about 0.8% or less, about 0.6% or less, about0.5% or less, about 0.4% or less or about 0.2% or less. In someembodiments, the strain-to-failure of the film 110 may be lower thanthat the strain-to-failure of the strengthened glass substrates 120 thathave a surface compressive stress greater than 500 MPa and a compressivedepth of layer greater than about 15 μm. In one or more embodiments, thefilm 110 may have a strain-to-failure that is at least 0.1% lower orless, or in some cases, at least 0.5% lower or less than thestrain-to-failure of the glass substrate 120. In one or moreembodiments, the film 110 may have a strain-to-failure that is at least0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.55%, 0.6%, 0.65%, 0.7%,0.75%, 0.8%, 0.85%, 0.9%, 0.95% or 1% lower or less than thestrain-to-failure of the glass substrate 120.

Exemplary films 110 may have a modulus of at least 25 GPa and/or ahardness of at least 1.75 GPa, although some combinations outside ofthis range are possible. In some embodiments the film 110 may have amodulus 50 GPa or greater or even 70 GPa or greater. For example, thefilm modulus may be 55 GPa, 60 GPa, 65 GPa, 75 GPa, 80 GPa, 85 GPa ormore. In one or more embodiments, the film 110 may have a hardnessgreater than 3.0 GPa. For example, the film 110 may have a hardness of 5GPa, 5.5 GPa, 6 GPa, 6.5 GPa, 7 GPa, 7.5 GPa, 8 GPa, 8.5 GPa, 9 GPa, 9.5GPa, 10 GPa or greater. These modulus and hardness values can bemeasured for such films 110 using known diamond nano-indentation methodsthat are commonly used for determining the modulus and hardness offilms. Exemplary diamond nano-indentation methods may utilize aBerkovich diamond indenter.

The films 110 described herein may also exhibit a fracture toughnessless than about 10 MPa·m^(1/2), or in some cases less than 5MPa·m^(1/2), or in some cases less than 1 MPa·m^(1/2). For example, thefilm may have a fracture toughness of 4.5 MPa·m^(1/2), 4 MPa·m^(1/2),3.5 MPa·m^(1/2), 3 MPa·m^(1/2), 2.5 MPa·m^(1/2), 2 MPa·m^(1/2), 1.5MPa·m^(1/2), 1.4 MPa·m^(1/2), 1.3 MPa·m^(1/2), 1.2 MPa·m^(1/2), 1.1MPa·m^(1/2), 0.9 MPa·m^(1/2), 0.8 MPa·m^(1/2), 0.7 MPa·m^(1/2), 0.6MPa·m^(1/2), 0.5 MPa·m^(1/2), 0.4 MPa·m^(1/2), 0.3 MPa·m^(1/2), 0.2MPa·m^(1/2), 0.1 MPa·m^(1/2) or less.

The films 110 described herein may also have a critical strain energyrelease rate (G_(IC)=K_(IC) ²/E) that is less than about 0.1 kJ/m², orin some cases less than 0.01 kJ/m². In one or more embodiments, the film110 may have a critical strain energy release rate of 0.09 kJ/m², 0.08kJ/m², 0.07 kJ/m², 0.06 kJ/m², 0.05 kJ/m², 0.04 kJ/m², 0.03 kJ/m², 0.02kJ/m², 0.0075 kJ/m², 0.005 kJ/m², 0.0025 kJ/m² or less.

In one or more embodiments, the film 110 may include a plurality oflayers. Each of the layers of the film may be characterized as brittlebased on one or more of the layer's impact on the average flexuralstrength of the article and/or the layer's strain-to-failure, fracturetoughness, or critical strain energy release rate values, as otherwisedescribed herein. In one variant, the layers of the film 110 need nothave identical properties such as modulus and/or fracture toughness. Inanother variant, the layers of the film 110 may include differentmaterials from one another.

In one or more embodiments, the film 110 may have a tensile stress thatwas built in the film or introduced into the film during deposition orformation. In some cases, the tensile stress into the film 110 may bedifficult to avoid while retaining the other desired properties. Thistensile stress can cause a film 110 to crack or fail more readily, forexample, in some cases this tensile stress may lower thestrain-to-failure (crack onset strain) of the film 110. Moreover, cracksoriginating in the film 110 can bridge more readily from the film 110into the glass substrate 120 under the right conditions, due in part tothe tensile stress. Additionally or alternatively, the tensile stress inthe film 110 may cause the a film 110 to crack or fail more readilybecause cracks originating in the glass substrate 120 can bridge morereadily from the glass substrate 120 into the film 110 under the rightconditions. As will be described in greater detail below, the crackmitigating layer 130 may allow the film 110 to relax during depositionor formation, where the film is disposed on the glass substrate 120after the crack mitigating layer 130 is disposed on the glass substrate120. Additionally or alternatively, the crack mitigating layer 130 mayreduce the amount of stress that is created locally in the film 110during loading (i.e., during the application of an external force on thefilm, such as the flexure experienced by the film during ring-on-ringtesting), or during flexure of the article 100.

The compositions or material(s) of the film 110 are not particularlylimited. Some non-limiting examples of film 110 materials include oxidessuch as SiO₂, Al₂O₃, TiO₂, Nb₂O₅, Ta₂O₅; oxynitrides such asSiO_(x)N_(y), SiAl_(x)O_(y)N_(z), and AlO_(x)N_(y); nitrides such asSiN_(x), AlN_(x), cubic boron nitride, and TiN_(x); carbides such asSiC, TiC and WC, semiconductor materials such as Si and Ge; transparentconductors such as indium-tin-oxide, tin oxide, fluorinated tin oxide,aluminum zinc oxide, or zinc oxide; carbon nanotube or graphene-dopedoxides; silver or other metal-doped oxides; highly siliceous polymerssuch as highly cured siloxanes and silsesquioxanes; diamond ordiamond-like-carbon materials; or selected metal films which can exhibita brittle fracture behavior.

The film 110 can be disposed on the glass substrate 120 by vacuumdeposition techniques, for example, chemical vapor deposition (e.g.,plasma enhanced chemical vapor deposition or atmospheric pressurechemical vapor deposition), physical vapor deposition (e.g., reactive ornonreactive sputtering or laser ablation), thermal, resistive, or e-beamevaporation, or atomic layer deposition. The film 110 may also bedisposed on one or more surfaces 122, 124 of the glass substrate 120using liquid-based techniques, for example sol-gel coating or polymercoating methods, for example spin, spray, slot draw, slide, wire-woundrod, blade/knife, air knife, curtain, gravure, and roller coating amongothers. In some embodiments it may be desirable to use adhesionpromoters, such as silane-based materials, between the film 110 and theglass substrate 120, between the glass substrate 120 and crackmitigating layer 130, between the layers (if any) of the crackmitigating layer 130, between the layers (if any) of the film 110 and/orbetween the film 110 and the crack mitigating layer 130. In one or morealternative embodiments, the film 110 may be disposed on the glasssubstrate 120 as a transfer layer.

The film 110 thickness can vary depending on the intended use of thearticle 100. In one embodiment the film 110 thickness may be in theranges from about 0.01 μm to about 0.5 μm or from about 0.01 μm to about20 μm. In another embodiment, the film 110 may have a thickness in therange from about 0.05 μm to about 10 μm, from about 0.05 μm to about 0.5μm, from about 0.01 μm to about 0.15 μm or from about 0.015 μm to about0.2 μm.

In some embodiments it may be advantageous to include a material in thefilm 110 that has either:

(1) a refractive index that is similar to the refractive index of eitherthe glass substrate 120, the crack mitigating layer 130 and/or otherfilms or layers in order to minimize optical interference effects;

(2) a refractive index (real and/or imaginary components) that is tunedto achieve anti-reflective interference effects; and/or

(3) a refractive index (real and/or imaginary components) that is tunedto achieve wavelength-selective reflective or wavelength-selectiveabsorptive effects, such as to achieve UV or IR blocking or reflection,or to achieve coloring/tinting effects.

In one or more embodiments, the film 110 may have a refractive indexthat is greater than the refractive index of the glass substrate 120and/or greater than the refractive index of the crack mitigating layer130. In one or more embodiments, the film may have a refractive index inthe range from about 1.7 to about 2.2, or in the range from about 1.4 toabout 1.6, or in the range from about 1.6 to about 1.9.

The film 110 may also serve multiple functions, or be integrated withfilms or layers that serve other functions than the film 110 or even thesame function(s) as the film 110. The film 110 may include UV or IRlight reflecting or absorbing layers, anti-reflection layers, anti-glarelayers, dirt-resistant layers, self-cleaning layers, scratch-resistantlayers, barrier layers, passivation layers, hermetic layers,diffusion-blocking layers, fingerprint-resistant layers, and the like.Further, the film 110 may include conducting or semi-conducting layers,thin film transistor layers, EMI shielding layers, breakage sensors,alarm sensors, electrochromic materials, photochromic materials, touchsensing layers, or information display layers. The film 110 and/or anyof the foregoing layers may include colorants or tint. When informationdisplay layers are integrated into the article 100, the article 100 mayform part of a touch-sensitive display, a transparent display, or aheads-up display. It may be desirable that the film 110 performs aninterference function, which selectively transmits, reflects, or absorbsdifferent wavelengths or colors of light. For example, the films 110 mayselectively reflect a targeted wavelength in a heads-up displayapplication.

Functional properties of the film 110 may include optical properties,electrical properties and/or mechanical properties, such as hardness,modulus, strain-to-failure, abrasion resistance, mechanical durability,coefficient of friction, electrical conductivity, electricalresistivity, electron mobility, electron or hole carrier doping, opticalrefractive index, density, opacity, transparency, reflectivity,absorptivity, transmissivity and the like. These functional propertiesare substantially maintained or even improved after the film 110 iscombined with the glass substrate 120, crack mitigating layer 130 and/orother films included in the article 100.

Crack Mitigating Layer

The crack mitigating layer 130 according to one or more embodiments mayhave a critical strain energy release rate (G_(IC)=K_(IC) ²/E) that isgreater than the critical strain energy release rate of the film 110. Inone or more embodiments, the film 110 may have a critical strain energyrelease rate of about 0.1 kJ/m² or less and the crack mitigating layer130 may have a critical strain energy release rate of greater than about0.1 kJ/m². The crack mitigating layer 130 may have a critical strainenergy release rate of about 1.0 kJ/m² or greater. In specificembodiments, the crack mitigating layer 130 may have a critical strainenergy release rate in a range of about 0.05 kJ/m² to about 100 kJ/m²,while the film 110 may have a critical strain energy release rate lessthan about 0.05 kJ/m². The crack mitigating layer 130 may have acritical strain energy release rate in the range from about 0.05 kJ/m²to about 90 kJ/m², from about 0.5 kJ/m² to about 80 kJ/m², from about0.5 kJ/m² to about 70 kJ/m², from about 0.5 kJ/m² to about 60 kJ/m²,from about 0.5 kJ/m² to about 50 kJ/m², from about 0.5 kJ/m² to about 40kJ/m², from about 0.5 kJ/m² to about 30 kJ/m², from about 0.5 kJ/m² toabout 20 kJ/m², from about 0.5 kJ/m² to about 10 kJ/m², from about 0.5kJ/m² to about 5 kJ/m², from about 1 kJ/m² to about 100 kJ/m², fromabout 5 kJ/m² to about 100 kJ/m², from about 10 kJ/m² to about 100kJ/m², from about 20 kJ/m² to about 100 kJ/m², from about 30 kJ/m² toabout 100 kJ/m², from about 40 kJ/m² to about 100 kJ/m², from about 50kJ/m² to about 100 kJ/m², from about 60 kJ/m² to about 100 kJ/m², fromabout 70 kJ/m² to about 100 kJ/m², from about 80 kJ/m² to about 100kJ/m², from about 90 kJ/m² to about 100 kJ/m², from about 0.05 kJ/m² toabout 1 kJ/m², from about 1 kJ/m² to about 5 kJ/m², from about 5 kJ/m²to about 10 kJ/m², from about 10 kJ/m² to about 20 kJ/m², from about 20kJ/m² to about 30 kJ/m², from about 30 kJ/m² to about 40 kJ/m², fromabout 40 kJ/m² to about 50 kJ/m², from about 50 kJ/m² to about 60 kJ/m²,from about 60 kJ/m² to about 70 kJ/m², from about 70 kJ/m² to about 80kJ/m² and from about 80 kJ/m² to about 90 kJ/m².

In such embodiments, the crack mitigating layer 130 has a greatercritical strain energy release rate than the film 110 and, therefore,can release strain energy from a crack bridging from one of the film 110and the glass substrate 120 into the other of the film 110 and the glasssubstrate 120. Such strain energy release stops the crack from bridgingacross the interface between the film 110 and the glass substrate 120.In one or more embodiments, the crack mitigation mechanism(s) describedherein occur regardless of where the crack originates (i.e., the film110 or the glass substrate 120).

In accordance with one or more embodiments, the crack mitigating layer130 may have an average strain-to-failure that is greater than theaverage strain-to-failure of the film 110. In one or more embodiments,the crack mitigating layer 130 may have an average strain-to-failurethat is equal to or greater than about 0.5%, 0.7%, 1%, 1.5%, 2%, or even4%. The crack mitigating layer 130 may have an average strain-to-failureof 0.6%, 0.8%, 0.9%, 1.1%, 1.2%, 1.3%, 1.4%, 1.6%, 1.7%, 1.8%, 1.9%,2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 5% or 6% or greater.In one or more embodiments, the film 110 may have an averagestrain-to-failure (crack onset strain) that is 1.5%, 1.0%, 0.7%, 0.5%,or even 0.4% or less. The film 110 may have an average strain-to-failureof 1.4%, 1.3%, 1.2%, 1.1%, 0.9%, 0.8%, 0.6%, 0.3%, 0.2%, 0.1% or less.The average strain-to-failure of the glass substrate 120 may be greaterthan the average strain-to-failure of the film 110, and in someinstances, may be greater than the average strain-to-failure of thecrack mitigating layer 130. In some specific embodiments, the crackmitigating layer 130 may have a higher average strain-to-failure thanthe glass substrate, to minimize any negative mechanical effect of thecrack mitigating layer on the glass substrate.

In one or more embodiments, the crack mitigating layer 130 may have afracture toughness of 1 MPa·m^(1/2) or greater, for example 2MPa·m^(1/2) or greater, or 5 MPa·m^(1/2) or greater. The crackmitigating layer 130 may also have a fracture toughness in the rangefrom about 1 MPa·m^(1/2) to about 5 MPa·m^(1/2), or from about 2MPa·m^(1/2) to about 4 MPa·m^(1/2). In one or more specific embodiments,the crack mitigating layer 130 may have a fracture toughness of 6MPa·m^(1/2), 7 MPa·m^(1/2), 8 MPa·m^(1/2), 9 MPa·m^(1/2), 10 MPa·m^(1/2)or greater. In such embodiments, the crack mitigating layer 130 averagestrain-to-failure and/or fracture toughness properties prevents thecrack from bridging across the interface between the film 110 and theglass substrate 120. In one or more embodiments, this crack mitigationmechanism occurs regardless of where the crack originates (i.e., thefilm 110 or the glass substrate 120).

The crack mitigating layer 130 may have a refractive index that isgreater than the refractive index of the glass substrate 120. In one ormore embodiments, the refractive index of the crack mitigating layer 130may be less than the refractive index of the film 110. In a morespecific embodiment, the refractive index of the crack mitigating layer130 may be between the refractive index of the glass substrate 120 andthe film 110. For example, the refractive index of the crack mitigatinglayer 130 may be in the range from about 1.45 to about 1.95, from about1.5 to about 1.8, or from about 1.6 to about 1.75. Alternatively, thecrack mitigating layer may have a refractive index that is substantiallythe same as the glass substrate, or a refractive index that is not morethan 0.05 index units greater than or less than the glass substrate overa substantial portion of the visible wavelength range (e.g. from 450 to650 nm).

In one or more embodiments, the crack mitigating layer 130 is able towithstand high temperature processes. Such processes can include vacuumdeposition processes such as chemical vapor deposition (e.g., plasmaenhanced chemical vapor deposition), physical vapor deposition (e.g.,reactive or nonreactive sputtering or laser ablation), thermal or e-beamevaporation and/or atomic layer deposition. In one or more specificembodiments, the crack mitigating layer is able to withstand a vacuumdeposition process in which the film 110 and/or other films disposed onthe glass substrate 120 are deposited on the crack mitigating layer 130via vacuum deposition. As used herein, the term “withstand” includes theresistance of the crack mitigating layer 130 to temperatures exceeding100° C., 200° C., 300° C., 400° C. and potentially even greatertemperatures. In some embodiments, the crack mitigating layer 130 may beconsidered to withstand the vacuum deposition process if the crackmitigating layer 130 experiences a weight loss of 10% or less, 8% orless, 6% or less, 4% or less, 2% or less or 1% or less, after depositionof the film 110 and/or other films on the glass substrate (and on thecrack mitigating layer 130). The deposition process (or testing afterthe deposition process) under which the crack mitigating layerexperiences weight loss can include temperatures of about 100° C. orgreater, 200° C. or greater, 300° C. or greater, 400° C. or greater;environments that are rich in a specific gas (e.g., oxygen, nitrogen,argon etc.); and/or environments in which deposition may be performedunder vacuum (10 Torr), under atmospheric conditions and/or at pressurestherebetween (e.g., 10 mTorr). As will be discussed herein, the materialutilized to form the crack mitigating layer 130 may be specificallyselected for its high temperature tolerances (i.e., the ability towithstand high temperature processes such as vacuum depositionprocesses) and/or its environmental tolerances (i.e., the ability towithstand environments rich in a specific gas or at a specificpressure). These tolerances may include high temperature tolerance, highvacuum tolerance, low vacuum outgassing, a high tolerance to plasma orionized gases, a high tolerance to ozone, a high tolerance to UV, a hightolerance to solvents, or a high tolerance to acids or bases. In someinstances, the crack mitigating layer 130 may be selected to pass anoutgassing test according to ASTM E595.

In one or more embodiments, the crack mitigating layer 130 preventsdegradation of the average flexural strength of the glass substrate 120.In another embodiment, the crack mitigating layer 130 prevents the film110 from degrading the average flexural strength of the glass substrate120. The crack mitigating layer 130 may prevent cracks from bridgingbetween the film 110 and the glass substrate 120. The crack mitigatinglayer 130 of one or more embodiments may increase the averagestrain-to-failure of the film 110 and thus, prevents degradation of theaverage flexural strength of the glass substrate 120. In one or morealternative embodiments, the crack mitigating layer 130 increases theaverage flexural strength of the article 100, when compared to articlesthat do not include such a crack mitigating layer but include a glasssubstrate and a film, as described herein.

The crack mitigating layer 130 may prevent degradation of the averagestrain-to-failure of the glass substrate 120 in some instances, while inother instances, the crack mitigating layer 130 may prevent the film 110from degrading the average strain-to-failure of the glass substrate 120.In another embodiment, the crack mitigating layer 130 prevents cracksfrom bridging between the film 110 and the glass substrate 120, thuspreventing the film 110 from degrading the average strain-to-failure ofthe glass substrate 120. In one or more alternative embodiments, thecrack mitigating layer 130 increases the average strain-to-failure ofthe article 100, when this average strain-to-failure is compared to theaverage strain-to-failure of articles that do not include a crackmitigating layer but include a glass substrate and a film, as describedherein.

In one or more embodiments, the crack mitigating layer 130 may have alow-modulus and/or low-hardness. Low modulus materials and low hardnessmaterials substantially overlap as many low modulus materials are alsolow hardness materials. However, these two properties (i.e., low modulusand low hardness) are distinguished herein because they highlight twodifferent mechanisms or methods by which a crack can be mitigated (i.e.,deflected, arrested or blunted) at the interface between the film 110and the glass substrate 120. The crack mitigating layer 130 may have amodulus so low that the crack mitigating layer 130 is unable to drive orpropagate a crack from one of the film 110 and glass substrate 120 tothe other of the film 110 and glass substrate 120. Such crack mitigatinglayers may have a modulus that is about less than about 50 GPa, lessthan about 30 GPa, less than about 15 GPa or even less than about 5 GPa.

The crack mitigating layer 130 may have a hardness that is less thanabout 3.0 GPa, less than 2.0 GPa or even less than 1.0 GPa. Thesemodulus and hardness values can be measured using known diamondnano-indentation methods that are commonly used for determining themodulus and hardness of films. Exemplary diamond nano-indentationmethods utilize a Berkovich diamond indenter.

In one or more embodiments, the crack mitigating layer 130 may alsoexhibit a low yield stress, a low shear modulus, plastic or ductiledeformation, or other known properties for strain energy release withoutbrittle fracture. In embodiments where the crack mitigating layerexhibits a low yield stress, the yield stress may be less than 500 MPa,less than 100 MPa, or even less than 10 MPa.

In embodiments in which the crack mitigating layer exhibits a lowmodulus, low yield stress, or plastic and/or ductile deformationbehavior, the crack mitigating layer 130 can deform to release strainenergy and prevent crack bridging or propagation between the film 110and glass substrate 120. These ductile crack mitigating layers may alsocomprise the high strain-to-failure values listed above for the crackmitigating layer.

An exemplary crack mitigating layer 130 may be a polymeric film. Suchfilms may have a low modulus or a low Tg that cannot support high valuesof stress within the deposited film 110, thus allowing the film 110 topartially relax and lower the tensile stress within, while minimizingthe transmission of stress fields into the glass substrate 120.

In one or more embodiments, the crack mitigating layer 130 physicallyprevents alignment of cracks originating in the film 110 and the glasssubstrate 120. In other words, a crack present in the film 110 cannotalign with a crack present in the glass substrate 120 because the crackmitigating layer 130 physically prevents such alignment. Alternately oradditionally, the crack mitigating layer 130 may have an engineeredmicrostructure that provides a tortuous path for crack propagation,providing an alternative path for strain energy release and minimizingor preventing crack bridging between the glass substrate 120 and film110.

In one or more embodiments, the crack mitigating layer 130 may include:porous oxides, such as SiO₂, Al₂O₃; TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, GeO₂ andsimilar material(s) known in the art; porous nitrides or carbides, forexample Si₃N₄, AlN, TiN, TiC; porous semiconductors such as Si or Ge;porous oxynitrides such as SiO_(x)N_(y), AlO_(x)N_(y), orSiAl_(x)O_(y)N_(z), tough or nanostructured inorganics, for example,zinc oxide, certain Al alloys, Cu alloys, steels, or stabilizedtetragonal zirconia; porous or non-porous hybrid organic-inorganicmaterials, for example, nanocomposites, fiber-reinforced polymers,silsesquioxanes, polysilsesquioxanes, or “ORMOSILs” (organicallymodified silica or silicate), and/or a variety of porous or non-porouspolymeric materials, for example siloxanes, polysiloxanes,polyacrylates, polyacrylics, PI (polyimides), polyamides, PIA(polyamideimides), polycarbonates, polysulfones, PSU or PPSU(polyarylsulfones), fluoropolymers, fluoroelastomers, lactams, polycylicolefins, and similar materials, including, but not limited to PDMS(polydimethylsiloxane), PMMA (poly(methyl methacrylate)), BCB(benzocyclobutene), PEI (polyethyletherimide), poly(arylene ethers) suchas PEEK (poly-ether-ether-ketone), PES (polyetheresulfone) and PAR(polyarylate), PET (polyethylene terephthalate), PEN (polyethylenenapthalate=poly(ethylene-2,6-napthalene dicarboxylate), FEP (fluorinatedethylene propylene), PTFE (polytetrafluoroethylene), PFA (perfluroalkoxypolymer, e.g., trade names Teflon®, Neoflon®) and similar materials.Other suitable materials include modified polycarbonates, some versionsof epoxies, cyanate esters, PPS (polyphenylsulfides), phyphenylenes,polypyrrolones, polyquinoxalines, and bismaleimides. In someembodiments, suitable polyacrylates can include poly(butyl acrylate). Insome cases it will be desirable to choose the high-temperature polymericmaterials such as siloxanes, silsesquioxanes, polyimides, BCB,fluoropolymers, and others listed herein or known in the art becausethese materials will tolerate a wider range of temperatures fordeposition and/or curing of the film 110. Examples of BCB polymersinclude the Cyclotene™ resins from Dow Chemical. Examples of polyimidesand polyimide precursors include Pyralin™ resins from HD Microsystems orelectronics grade polyamic acid solution from Sigma Aldrich (cat. no.431206). The polyimides may include fluorinated or non-fluorinatedpolyimides such as those disclosed in U.S. Pat. No. 5,325,219 andrelated references, or other work known in the art such as “Preparationand Properties of a High Temperature, Flexible and Colorless ITO CoatedPolyimide Substrate”, European Polymer Journal, 43, p. 3368, 2007;“Flexible Organic Electroluminescent Devices Based onFluorine-Containing Colorless Polyimide Substrates”, Advanced Materials,14, 18, p. 1275, 2002; and “Alignment layer effects on thin liquidcrystal cells,” Appl. Phys. Lett. 92, 061102, 2008. Examples ofsilsesquioxanes include Accuglass® Spin-on-Glasses from Honeywell orFOx® Flowable Oxides from Dow Corning.

The thickness of the crack mitigating layer 130 may be in the range ofabout 0.01 μm to about 10 μm (10 nm to 10,000 nm) or in the range fromabout 0.04 μm to about 0.5 μm (40 nm to about 500 nm); however in somecases the layer can be much thinner, for example, the crack mitigatinglayer 130 may be a single-molecule “monolayer” having a thickness ofabout 0.1 nm to about 2 nm. In one or more embodiments, the thickness ofthe crack mitigating layer 130 is in the range from about 0.02 μm toabout 10 μm, from about 0.03 μm to about 10 μm, from about 0.04 μm toabout 10 μm, from about 0.05 μm to about 10 μm, from about 0.06 μm toabout 10 μm, from about 0.07 μm to about 10 μm, from about 0.08 μm toabout 10 μm, from about 0.09 μm to about 10 μm, from about 0.1 μm toabout 10 μm, from about 0.01 μm to about 9 μm, from about 0.01 μm toabout 8 μm, from about 0.01 μm to about 7 μm, from about 0.01 μm toabout 6 μm, from about 0.01 μm to about 5 μm, from about 0.01 μm toabout 4 μm, from about 0.01 μm to about 3 μm, from about 0.01 μm toabout 2 μm, from about 0.01 μm to about 1 micron, from about 0.02 μm toabout 1 micron, from about 0.03 to about 1 μm, from about 0.04 μm toabout 0.5 μm, from about 0.05 μm to about 0.25 μm or from about 0.05 μmto about 0.15 μm.

In one or more embodiments, thicknesses of the glass substrate 120, film110 and/or crack mitigating layer 130 may be specified in relation toone another. For example, the crack mitigating layer may have athickness that is less than or equal to about 10 times the thickness ofthe film. For example, where a film 110 has a thickness of about 85 nm,the crack mitigating layer 130 may have a thickness of about 850 nm orless. In another example, the thickness of the crack mitigating layer130 may be in the range from about 35 nm to about 80 nm and the film 110may have a thickness in the range from about 30 nm to about 300 nm. Inone variant, the crack mitigating layer may have a thickness that isless than or equal to about 9 times, 8 times, 7 times, 6 times, 5 times,4 times, 3 times or two times the thickness of the film. In anothervariant, the thickness of the film and the thickness of the crackmitigating film are each less than about 10 μm, less than about 5 μm,less than about 2 μm, or less than about 1 μm. The ratio of the crackmitigating layer 130 thickness to the film 110 thickness may be, in someembodiments, in the range from about 1:2 to about 1:8, in the range fromabout 1:3 to about 1:6, in the range from about 1:3 to about 1:5, or inthe range from about 1:3 to about 1:4.

One or more embodiments of the article include a crack mitigating layer130 comprising polyimide. In such embodiments, when the crack mitigatinglayer 130 is utilized, the film 110 maintains functional properties(e.g., electrical conductivity) and the article 100 retains its averageflexural strength. In such embodiments, the film 110 may include one ormore transparent conductive oxide layers, such as indium-tin-oxidelayers. In addition, the glass substrate 120 may be strengthened, ormore specifically, chemically strengthened. In these embodiments, use ofpolyimide or other high-temperature-tolerant polymers as components ofthe crack mitigating layer may be preferred because thesehigh-temperature-tolerant polymers can withstand the sometimes harshvacuum deposition conditions of certain films, an important factor inenabling the desired film properties to be maintained.

Additionally or alternatively, the film 110 comprising indium-tin-oxideand the crack mitigating layer 130 comprising polyimide form a stack,wherein the stack has an overall low optical reflection. For example,the overall reflection of such a stack may be 10% or less, 8% or less,7% or less, 6.5% or less, 6% or less, 5.5% or less across a visiblewavelength range from 450-650 nm, 420-680 nm, or even 400-700 nm. Thereflectivity numbers above are quoted including the reflection from oneexternal bare (or uncoated) glass interface, as shown in the opticalreflectance simulations of FIGS. 10, 11, and 12, which is approximately4% reflection from the external uncoated glass interface alone, and forspecific embodiment where a polyimide crack mitigating layer 130 and anindium-tin-oxide film 110 are covered by some encapsulation or adhesivelayer. Thus, the reflectivity from this film stack structure andfilm-glass coated interfaces alone (subtracting out the reflectivity ofthe external, uncoated glass interface) is less than about 5%, 4%, 3%,2%, or even less than about 1.5% across a visible wavelength range from450-650 nm, 420-680 nm, or even 400-700 nm, when covered by a typicalencapsulant (i.e. an additional film or layer) having an encapsulantrefractive index of about 1.45-1.65.

The crack mitigating layer 130 may be disposed between the film 110 andthe glass substrate 120 by a variety of methods. The crack mitigatinglayer 130 can be disposed using vacuum deposition techniques, forexample, chemical vapor deposition (e.g., plasma enhanced chemical vapordeposition), physical vapor deposition (e.g., reactive or nonreactivesputtering or laser ablation), thermal, resistive or e-beam evaporationand/or atomic layer deposition. The crack mitigating layer 130 may alsobe disposed using liquid-based deposition techniques, for examplesol-gel coating or polymer coating methods, for example spin, spray,slot draw, slide, wire-wound rod, blade/knife, air knife, curtain,roller, gravure coating among others and other methods known in the art.Porosity can be also be introduced in the crack mitigating layer 130 tolower the overall crack mitigating layer 130 elastic modulus or providea tortuous path for crack propagation by various known methods such as aslight overpressure of gas in the vacuum chamber, low temperaturedeposition, use of porogens (materials that create pores or increaseporosity) in chemical vapor deposition processes, and plasma energymodification. Porosity can be introduced to liquid-based depositiontechniques by use of a pore forming material which is later dissolved orthermally decomposed, phase separation methods, or the casting of aparticulate or nanoparticulate film where interstices between particlesremain partially void.

Polymeric or organic-inorganic hybrid materials can be employed in thecrack mitigating layer 130 where it is desirable for the crackmitigating layer 130 to have ductile properties or to be plasticallydeformable, with or without porosity. In addition, the crack mitigatinglayer 130 may include ductile metal films such as Al or Cu.

In some embodiments a useful measure of tendency towards plasticdeformation is the elongation at break (expressed as a “%” or a “strainvalue”). In these embodiments the crack mitigating layer 130 may beductile or plastically deformable and may include material that exhibitsan elongation at break, strain value, greater than about 1%, greaterthan 2%, greater than 5%, or even greater than 10%. The crack mitigatinglayer 130 may have a higher elongation to break than the film 110.Exemplary materials for use in crack mitigating layers 130 that areductile or plastically deformable include a variety of metals andpolymers, including organic-inorganic hybrids, materials listed aboveincluding, but not limited to, polyimides, PTFE(polytetrafluoroethylene), PES (polyethersulfone), PEI (polyetherimide),PPSU (polyphenylsulfone), PVDF (polyvinylidine difluoride), polyesters,and similar materials known in the art. In instances where a ductile orplastically deformable crack mitigating layer 130 is utilized, the crackmitigating layer 130 may also have a high toughness. For example, thecrack mitigating layer 130 may have a fracture toughness of 0.5MPa·m^(1/2) or greater, or in some cases 5 MPa·m^(1/2) or greater. Thecrack mitigating layer may also have a high critical strain energyrelease rate, with values as listed hereinabove.

In one or more embodiments, a crack mitigating layer 130 may haveductile or plastically deformable properties and/or can also be usedbetween the film 110 and the glass substrate 120 to create an engineeredadhesion between the film 110 and the glass substrate 120. In one ormore specific embodiments, the crack mitigating layer 130 creates alow-adhesion or low toughness layer or interface between the film 110and the glass substrate 120. In one variant the low-adhesion orlow-toughness layer or interface may have a toughness that is less thanabout 0.5 times the toughness of the glass substrate 120. The goal ofthe crack mitigating layer 130, when used to modify the adhesion orinterfacial toughness between the film 110 and glass substrate 120, isto form an adhesion that is high enough for normal use, but under highstress conditions, the interface between the film 110 and glasssubstrate 120 fails before cracks can bridge from one of the film 110 orthe glass substrate 120 into the other of the film 110 or the glasssubstrate 120. Stated another way, the film 110 delaminates from theglass substrate 120 under high stress conditions because the adhesion islow enough to energetically favor film delamination or crack deflectionalong one or more interfaces. In one or more embodiments, when the crackmitigating layer 130 is utilized to create an engineered adhesion, theinterface between the film 110 and the glass substrate has a criticalstrain energy release rate that is less than 0.25 times or less than 0.5times the critical strain energy release rate of the glass substrate. Insuch cases, the critical strain energy release rate of the interface canbe less than about 0.05 kJ/m², less than about 0.005 kJ/m², or even lessthan about 0.003 kJ/m², but in some embodiments may be greater thanabout 0.001 kJ/m².

In some embodiments the adhesion between the film 110 and the glasssubstrate 120 is modified by modifying the surface energy of the glasssubstrate 120. The surface energy of the glass substrate 120 can bemodified by disposing a material monolayer, a self-assembled materialmonolayer, a sub-monolayer (incomplete coverage), an islands-in-the-sealayer where a material layer constitutes the islands and the glasssurface the sea, or other very thin atomic or molecular-scale layers onthe glass substrate 120. These layers may be chosen to have a lowersurface energy than the glass substrate 120, or a lower bonding affinityfor either the glass substrate 120 or the film 110. Examples ofmaterials useful in such layers may include the aforementioned nitrides,carbides, hybrid organic-inorganic silanes or silazanes orsilsesquioxanes, polymeric or monomeric organics, and similar materials.Specific examples, in addition to those listed previously, include butare not limited to boron nitride, graphene, graphitic carbon, glassycarbon, diamond-like carbon, hexamethyldisilazane (HMDS),trimethlyethoxysilane, fluorosilanes, fluorocarbons, and similar orrelated materials. The adhesion-modifying materials applied to the glasssubstrate 120 may have a thickness in the range of 1-10 atomic ormolecular layers, or in other cases a thickness in the range of 0.1 to10 nanometers. However, as described, in some cases theadhesion-modifying layer may serve a dual function as a crack mitigatinglayer 130, for example having both dual adhesion modifying and plasticdeformation properties. In such instances, the thickness can be greater,such as that described above for the crack mitigating layer 130.

In an embodiment, the materials utilized to modify the surface energy ofthe glass substrate 120 may be disposed in a controlled fashion toachieve tunable or incomplete surface coverage on the glass substrate120 as a method to tune the adhesion into a desired range. Alternately,wet chemistry methods can also be used, particularly for the organicallymodified materials. Another method for creating tunable surface coverageof these materials, for example the above mentioned silanes orsilazanes, is to deposit a thin film of the material with completecoverage and then treat the film for a short time in the range of 0.5minutes to 120 minutes at high temperature in the range of 100-600° C.in oxygen or under an oxygen plasma. By controlling the time of heatingor plasma treatment, the silanes or silazanes have some of their organicgroups removed or converted to SiO₂, thus creating an intermediate andtunable surface energy or adhesion level.

An additional or alternative approach for creating engineered adhesionbetween the film 110 and the glass substrate 120, is to control thedeposition conditions of the film 110. For example, using lowtemperature or low plasma energy during a vapor deposition processes,the bonding strength between the film 110 and the glass substrate 120can be reduced in a controlled fashion owing to molecular/atomic organicspecies, molecular/atomic metallic species, or incomplete ionic orincomplete covalent bonding across the interface between the film 110and glass substrate 120. Such engineered adhesion interfaces may becharacterized by a high proportion of hydrogen bonding or Van der Waalsbonding, relative to covalent or ionic bonding, at the interface betweenfilm 110 and glass substrate 130. In one or more embodiments, suchprocess conditions may be useful with certain films 110 that can bedisposed at low temperature or low plasma energy without adverselyaffecting the functional properties of the film itself.

The optical properties of the article 100 may be adjusted by varying oneor more of the properties of the film 110, crack mitigating layer 130and/or the glass substrate 120. For example, the article 100 may exhibita total reflectance of 10% or less, 8% or less, 7% or less, 6.9% orless, 6.8% or less, 6.7% or less, 6.6% or less, 6.5% or less, 6.4% orless, 6.3% or less, 6.2% or less, 6.1% or less and/or 6% or less, overthe visible wavelength range from about 400 nm to about 700 nm. Rangesmay further vary as specified hereinabove, and ranges for the filmstack/coated glass interfaces alone are listed hereinabove. In morespecific embodiments, the article 100 described herein, may exhibit alower average reflectance and greater average flexural strength thanarticles without a crack mitigating layer 130. In one or morealternative embodiments, at least two of optical properties, electricalproperties or mechanical properties of the article 100 may be adjustedby varying the thickness(es) of the glass substrate 120, film 110 and/orthe crack mitigating layer 130. Additionally or alternatively, theaverage flexural strength of the article 100 may be adjusted or improvedby modifying the thickness(es) of the glass substrate 120, film 110and/or the crack mitigating layer 130.

The article 100 may include one or more additional films disposed on theglass substrate. In one or more embodiments, the one or more additionalfilms may be disposed on the film 110 or on the opposite major surfacefrom the film. The additional film(s) may be disposed in direct contactwith the film 110. In one or more embodiments, the additional film(s)may be positioned between: 1) the glass substrate 120 and the crackmitigating layer 130; or 2) the crack mitigating layer 130 and the film110. In one or more embodiments, both the crack mitigating layer 130 andthe film 110 may be positioned between the glass substrate 120 and theadditional film(s). The additional film(s) may include a protectivelayer, an adhesive layer, a planarizing layer, an anti-splinteringlayer, an optical bonding layer, a display layer, a polarizing layer, alight-absorbing layer, reflection-modifying interference layers,scratch-resistant layers, barrier layers, passivation layers, hermeticlayers, diffusion-blocking layers and combinations thereof, and otherlayers known in the art to perform these or related functions. Examplesof suitable protective or barrier layers include layers containingSiO_(x), SiN_(y), SiO_(x)N_(y), other similar materials and combinationsthereof. Such layers can also be modified to match or complement theoptical properties of the film 110, the crack mitigating layer 130and/or the glass substrate 120. For example, the protective layer may beselected to have a similar refractive index as the crack mitigatinglayer 130, the film 110 or the glass substrate 120. It will be apparentto those of ordinary skill in the art that multiple additional film(s)with varying refractive indices and/or thicknesses can be inserted forvarious reasons. The refractive indices, thicknesses and otherproperties of the additional films (as well as the crack mitigatinglayer 130 and the film 110) may be further modified and optimized,without departing from the spirit of the disclosure. In other cases, forexample, alternate film designs can be employed where the crackmitigating layer 130 may have a higher refractive index than the film.In other cases, the crack mitigating layer 130 may be engineered to haveeven lower modulus or greater ductility or plasticity than theembodiments and examples disclosed herein.

In one or more embodiments, the articles 100 described may be used ininformation display devices and/or touch-sensing devices. In one or morealternative embodiments, the article 100 may be part of a laminatestructure, for example as a glass-polymer-glass laminated safety glassto be used in automotive or aircraft windows. An exemplary polymermaterial used as an interlayer in these laminates is PVB (Polyvinylbutyral), and there are many other interlayer materials known in the artthat can be used. In addition, there are various options for thestructure of the laminated glass, which are not particularly limited.The article 100 may be curved or shaped in the final application, forexample as in an automotive windshield, sunroof, or side window. Thethickness of the article 100 can vary, for either design or mechanicalreasons; for example, the article 100 can be thicker at the edges thanat the center of the article. The article 100 may be acid polished orotherwise treated to remove or reduce the effect of surface flaws.

Another aspect of the present disclosure pertains to touch-sensingdevices including the articles described herein. In one or moreembodiments, the touch sensor device may include a glass substrate 120(which may be strengthened or not strengthened), a film 110 comprising atransparent conductive oxide and a crack mitigating layer 130. Thetransparent conductive oxide may include indium-tin-oxide,aluminum-zinc-oxide, fluorinated tin oxide, or others known in the art.In one or more embodiments, the film 110 is discontinuously disposed onthe glass substrate 120. In other words, the film 110 may be disposed ondiscrete regions of the glass substrate 120. The discrete regions withthe film form patterned or coated regions (not shown), while thediscrete regions without the film form unpatterned or uncoated regions(not shown). In one or more embodiments, the patterned or coated regionsand unpatterned or uncoated regions are formed by disposing the film 110continuously on a surface of the glass substrate 120 and thenselectively etching away the film 110 in the discrete regions so thatthere is no film 110 in those discrete regions. The film 110 may beetched away using an etchant such as HCl or FeCl₃ in aqueous solutions,such as the commercially available TE-100 etchant from Transene Co. Inone or more embodiments, the crack mitigating layer 130 is notsignificantly degraded or removed by the etchant. Alternatively, thefilm 110 may be selectively deposited onto discrete regions of a surfaceof the glass substrate 120 to form the patterned or coated regions andunpatterned or uncoated regions.

In one or more embodiments, the uncoated regions have a totalreflectance that is similar to the total reflectance of the coatedregions. In one or more specific embodiments, the unpatterned oruncoated regions have a total reflectance that differs from the totalreflectance of the patterned or coated regions by about 5% or less, 4.5%or less, 4% or less, 3.5% or less, 3% or less, 2.5% or less, 2.0% orless, 1.5% or less or even 1% or less across a visible wavelength in therange from about 450 nm to about 650 nm, from about 420 nm to about 680nm or even from about 400 nm to about 700 nm.

In accordance with another aspect of the present disclosure, articles100 including both a crack mitigating layer 130 and a film 110, whichmay include indium-tin-oxide or other transparent conductive oxides,exhibit resistivity that is acceptable for use of such articles in touchsensing devices. In one or more embodiments, the films 110, when presentin the articles disclosed herein, exhibit a sheet resistance of about100 ohm/square or less, 80 ohm/square or less, 50 ohm/square or less, oreven 30 ohm/square or less. In such embodiments, the film may have athickness of about 200 nm or less, 150 nm or less, 100 nm or less, 80 nmor less, 50 nm or less or even 35 nm or less. In one or more specificembodiments, such films, when present in the article, exhibit aresistivity of 10×10⁻⁴ ohm-cm or less, 8×10⁻⁴ ohm-cm or less, 5×10⁻⁴ohm-cm or less, or even 3×10⁻⁴ ohm-cm or less. Thus, the films 110, whenpresent in the articles 100 disclosed herein can favorably maintain theelectrical and optical performance expected of transparent conductiveoxide films and other such films used in touch sensor applications,including projected capacitive touch sensor devices.

The disclosure herein can also be applied to articles which have aarticles that are not interactive or for display; for example, sucharticles may be used in a case in which a device has a glass front sidethat is used for display and can be interactive, and a back side thatmight be termed “decorative” in a very broad sense, meaning thatbackside can be “painted” some color, have art work or information aboutthe manufacturer, model and serial number, texturing or other features.

Another aspect of the present disclosure pertains to a method of formingan article 100. In one or more embodiments, such methods includeproviding a glass substrate 120, disposing a crack mitigating layer 130on a surface (e.g., one or more of the major surfaces 122, 124 and/orone or more minor surfaces) of the glass substrate 120, disposing a film110 on the crack mitigating layer 130, such that the crack mitigatinglayer 130 is disposed between the film 110 and the glass substrate 120.In one or more embodiments, the method includes disposing the film 110via a vacuum deposition process. In particular embodiments, such vacuumdeposition processes may utilize temperatures of at least about 100° C.,200° C., 300° C., 400° C. and all ranges and sub-ranges therebetween.

In one or more specific embodiments, the method includes controlling thethickness(es) of the crack mitigating layer 130 and/or the film 110.Controlling the thickness(es) of the films disclosed herein may beperformed by controlling one or more processes for forming the films sothat the films are applied having a desired or defined thickness. In aneven more specific embodiment, the method includes controlling thethickness(es) of the crack mitigating layer 130 and/or the film 110 tomaintain the average flexural strength of the glass substrate 120 and/orthe functional properties of the film 110. The method may includedisposing an additional film on the glass substrate 120. In one or moreembodiments, the method may include disposing the additional film on theglass substrate such that the additional film is disposed between theglass substrate 120 and the crack mitigating layer 130, between thecrack mitigating layer 130 and the film 110 or, such that the film 110is between the crack mitigating layer 130 and the additional film.Alternatively, the method may include disposing the additional film onthe opposite major surface of the glass substrate 120 from the surfaceon which the film is disposed. The additional film may include aprotective layer, an adhesive layer, a planarizing layer, ananti-splintering layer, an optical bonding layer, a display layer, apolarizing layer, a light-absorbing layer, reflection-modifyinginterference layers, scratch-resistant layers, barrier layers,passivation layers, hermetic layers, diffusion-blocking layers, orcombinations thereof.

In one or more embodiments, the method includes strengthening the glasssubstrate 120 before or after disposing the crack mitigating layer 130,film 110 and/or an additional film on the glass substrate. The glasssubstrate 120 may be strengthened chemically or otherwise. The glasssubstrate 120 may be strengthened after disposing the crack mitigatinglayer 130 on the glass substrate 120 but before disposing the film 110on the glass substrate. The glass substrate 120 may be strengthenedafter disposing the crack mitigating layer 130 and the film 110 on theglass substrate 120 but before disposing an additional film (if any) onthe glass substrate. Where no additional film is utilized, the glasssubstrate 120 may be strengthened after disposing the crack mitigatinglayer 130 and the film 110 on the glass substrate.

The following examples represent certain non-limiting embodiments of thedisclosure.

Examples 1A-1J

Examples 1A-1J include articles according to one or more embodiments ofthe present disclosure or glass substrates of the prior art. Each ofExamples 1A-1J utilized commercially available glass substrates ofaluminosilicate glass. The glass substrates had a thickness of 0.7 mm.In Examples 1A-1E, the glass substrates were strengthened by ionexchange to provide a surface compressive stress (CS) of about 690 MPaand a compressive depth of layer (DOL) of about 23 μm. The glasssubstrate of Example 1F was not strengthened by ion exchange. InExamples 1G-1J, the strengthened glass substrates were strengthened byion exchange to provide a surface compressive stress of about 740 MPaand a compressive depth of layer of about 44 μm. A crack mitigatinglayer comprising polyimide and/or a film comprising indium-tin-oxidewere disposed on the strengthened glass substrates and(non-strengthened) glass substrates as provided below in Table 1.Examples 1A, 1E, 1F, 1G and IH are indicated as comparative because theydid not include a crack mitigating layer.

TABLE 1 Examples 1A-1J. Crack Surface CS/ Mitigating Film GlassCompressive Layer (indium- Example Substrate DOL (polyimide) tin-oxide)1A Strengthened 690 MPa/23 μm none None (compar- ative) 1B Strengthened690 MPa/23 μm 155 nm 85 nm 1C Strengthened 690 MPa/23 μm 220 nm 85 nm 1DStrengthened 690 MPa/23 μm 290 nm 85 nm 1E Strengthened 690 MPa/23 μmNone 85 nm (compar- ative) 1F Not — None 85 nm (compar- ative) 1GStrengthened 740 MPa/44 μm None None (compar- ative) 1H Strengthened 740MPa/44 μm None 85 nm (Compar- ative) 1I Strengthened 740 MPa/44 μm 490nm 85 nm 1J Strengthened 740 MPa/44 μm  45 nm 85 nm

For the Examples including a strengthened glass substrate (i.e.,Examples 1A-1E and 1G-1J), the ion-exchange process was carried out byimmersing the glass substrate in a molten potassium nitrate (KNO₃) baththat was heated to a temperature in the range from about 350° C. to 450°C. The glass substrates were immersed in the bath for a duration of 3-8hours to achieve the surface CS and compressive DOL provided in Table 1.After completing the ion exchange process, the glass substrates ofExamples 1A-1E and 1G-1J were cleaned in a 1-4% concentration KOHdetergent solution, supplied by Semiclean KG, having a temperature of50-70° C. The detergent solution was ultrasonically agitated at 40-110KHz. The strengthened glass substrates were then rinsed in DI water,which was also ultrasonically agitated at 40-110 KHz and thereafterdried. Example 1F was also cleaned, rinsed and dried in the same manneras Examples 1A-1E and 1G-1J. In the Examples where a crack mitigatinglayer was utilized, the following procedure was employed. Prior todisposing the crack mitigating layer, the strengthened glass substrateswere then baked for 10 minutes on a hot plate at a temperature of 130°C., and then removed to cool for about 2 minutes.

An aminosilane-based adhesion promoter (supplied by HD Microsystemsunder the name VM-652) was applied to the strengthened and glasssubstrates and allowed to remain in the wet state for 20 seconds. Theadhesion promoter was spun off the strengthened glass substrates, byspinning the glass substrate and the adhesion promoter applied thereonin a standard vacuum-chuck spin coater at 5000 RPM. After application ofthe adhesion promoter, a solution of polyimide (supplied by HDMicrosystems under the name PI-2555) previously diluted with a solventthinner comprising N-methyl-2-pyrrolidone (supplied by HD Microsystemsunder the name T9038/9), using various volume ratios as set out below,was applied to the strengthened glass substrates. About 1 mL of thepolymer solution was applied to each glass sample measuring 50×50 mmsquare. The strengthened glass substrates with the polyimide solutionwere then spun at 500 RPM for 3-5 seconds, followed by subsequentrotation of 500-5000 RPM for 30-90 seconds, followed by an optionalfinal rotation step at 5000 RPM for 15 seconds, to obtain the desiredthickness and/or concentration of the crack mitigating layer. Example 1Bhad a polyimide thickness of 155 nm and was prepared using polyimidesolution diluted in a 30:70 ratio with the solvent thinner and was spunfirst at a rotation of 500 RPM for 3 seconds, followed by a subsequentrotation at 4000 RPM for 60 seconds. Example 1C had a polyimidethickness of 220 nm and was prepared using polyimide solution diluted ina 30:70 ratio with the solvent thinner and was spun first at a rotationof 500 RPM for 3 seconds, followed by a subsequent rotation at 1500 RPMfor 90 seconds. Example 1D had a polyimide thickness of 290 nm and wasprepared using polyimide solution diluted in a 40:60 ratio with thesolvent thinner and was spun first at a rotation of 500 RPM for 3seconds, followed by a subsequent rotation at 1000 RPM for 90 seconds.For examples 1B-1D, the polymer solutions were applied and spin coatedon the glass substrates when the solutions were at a temperature ofabout 15° C., which tends to slow the evaporation of the solvent andyield somewhat thinner films than with a higher temperature solution.Example 11 had a polyimide thickness of 490 nm and was prepared usingpolyimide solution diluted in a 50:50 ratio with the solvent thinner andwas spun first at a rotation of 500 RPM for 5 seconds, followed by asubsequent rotation at 1500 RPM for 45 seconds, followed by a finalrotation at 5000 RPM for 15 seconds. Example 1J had a polyimidethickness of 45 nm and was prepared using polyimide solution diluted ina 20:80 ratio with the solvent thinner and was spun first at a rotationof 500 RPM for 5 seconds, followed by a subsequent rotation at 2000 RPMfor 30 seconds, followed by a final rotation at 5000 RPM for 15 seconds.For examples 11 and 1J, the polymer solutions were allowed toequilibrate at room temperature (i.e., about 25° C.) for at least onehour before applying and spin coating the solutions on the glasssubstrates.

Immediately after the spin coating steps as outline above, the Examplescontaining a crack mitigating layer were then dried and baked on a hotplate at a temperature of 130° C. for 2-3 minutes and then placed in anN₂ curing oven (supplied by YES) operating at a pressure of 280 torr andcured at a temperature of 240° C. for 90 minutes. Based on known dataand information obtained by testing, the resulting crack mitigatinglayer had an elastic modulus of about 2.5 GPa to about 10 GPa and anelongation to break of about 10% after curing.

An indium-tin-oxide-containing film was applied to the Examples, asindicated in Table 1. The indium-tin-oxide film was sputtered from anoxide target, using a system supplied by KDF, under the name model 903i.The sputtering target was also supplied by KDF and included SnO₂ andIn₂O₃ present at a ratio of 10:90 by weight. The film was sputtered at apressure of 10 mTorr in the presence of oxygen flowed at a rate of about0.5 sccm and argon flowed at a rate of 30 sccm, with DC power suppliedat 600 W. After the film was disposed, as indicated in Table 1, theExamples were annealed at a temperature of about 200° C. for 60 minutesin air. For the Examples which did not include a crack-mitigating film(i.e., Examples 1E, 1F, and 1H), the glass substrate was pre-treated,before deposition of the film using a plasma cleaning step in the sameKDF system, where the plasma cleaning step employed 15 mTorr pressure,50 sccm of Argon flow, 5 sccm of oxygen flow, and 400 W of RF power for1 minute.

To demonstrate the retention of average flexural strength of thearticles and strengthened glass substrates of Examples 1A-1J, thearticles and glass substrates were tested using ring-on-ring load tofailure testing, as shown in FIG. 5. For ring-on-ring load to failuretesting, Examples 1B-1F and 1H-1J (with the film and/or crack mitigatinglayer) were tested with the side with the film and/or crack mitigatinglayer in tension. For Examples 1A and 1G (without a film or crackmitigating layer), one side of the strengthened glass substrate wassimilarly in tension. The ring-on-ring load to failure testingparameters included a contact radius of 1.6 mm, a cross-head speed of1.2 mm/minute, a load ring diameter of 0.5 inches, and a support ringdiameter of 1 inch. Before testing, an adhesive film was placed on bothsides of the articles and strengthened glass substrates to containbroken glass shards.

As illustrated in FIG. 5, the addition of a crack mitigating layerincluding polyimide, having a thickness in the range from about 45 nm toabout 490 nm, resulted in articles that retained about the same averageflexural strength as glass substrates without a crack mitigating layeror film. Moreover, the articles with a crack mitigating layer exhibitedgreater average flexural strength than the strengthened andnon-strengthened glass substrates with only a film. For comparison, thestrengthened and non-strengthened glass substrates with only a filmdisposed thereon (i.e., Examples 1E, 1F and 1H) exhibited a substantialreduction in the average flexural strength.

Examples 2A-2D

Each of Examples 2A-2D utilized glass substrates that included acomposition of 61 mol %≤SiO₂≤75 mol %; 7 mol %≤Al₂O₃≤15 mol %; 0 mol%≤B₂O₃≤12 mol %; 9 mol %≤Na₂O≤21 mol %; 0 mol %≤K₂O≤4 mol %; 0 mol%≤MgO≤7 mol %; 0 mol %≤CaO≤3 mol %, and 0 mol %≤SnO₂≤1 mol %. The glasssubstrates had a thickness of 0.7 mm and were strengthened by ionexchange and prepared for combination with a crack mitigating layerand/or film, using the same processes as described with reference toExamples 1A-1J. The strengthened glass substrates of Examples 2A-2D hada surface compressive stress (CS) of about 776 MPa and a compressivedepth of layer (DOL) of about 41.4 μm. A crack mitigating layercomprising polyimide and a film comprising indium-tin-oxide weredisposed on the strengthened glass substrates as provided below in Table2, using the methods described with reference to Examples 1A-1J toprovide the articles of Examples 2A-2D. An adhesion promoter wasutilized in the same manner as Examples 1B-1D, 1I, and 1J. Example 2Ahad a polyimide thickness of 250 nm and was prepared using polyimidesolution diluted in a 30:70 volume ratio with the solvent thinner andwas spun first at a rotation of 500 RPM for 3 seconds, followed by asubsequent rotation at 4000 RPM for 60 seconds. Example 2B had apolyimide thickness of 90 nm and was prepared using polyimide solutiondiluted in a 20:80 volume ratio with the solvent thinner and was spunfirst at a rotation of 500 RPM for 3 seconds, followed by a subsequentrotation at 4000 RPM for 60 seconds. For examples 2A and 2B, the polymersolutions were allowed to equilibrate at room temperature (i.e., about25 C) for at least one hour before applying and spin coating thesolutions on the glass substrates. Drying, baking and curing for thesepolyimide-coated samples was carried out in the same manner as examples1B-1D, 1I, and 1J. Examples 2C and 2D are indicated as comparativebecause they did not include a crack mitigating layer.

TABLE 2 Examples 2A-2D. Crack mitigating Film Example layer (polyimide)(indium-tin-oxide) 2A 250 nm 85 nm 2B  90 nm 85 nm 2C None 85 nm(comparative) 2D None None (comparative)

For ball drop height-to-failure testing, the articles of Examples 2A-2C(with the film and/or crack mitigating layer) were tested with the sidewith the film and/or crack mitigating layer in tension. For Example 2D,without a film or crack mitigating layer, one side of the strengthenedglass substrate was similarly in tension. A steel ball having a weightof 128 g and diameter of 31.75 mm was utilized. The articles and thestrengthened glass substrate each had a size of 50 mm×50 mm and weresupported at each edge. Before testing, an adhesive film was placed onboth sides of the articles and the strengthened glass substrate tocontain broken glass shards.

As illustrated in FIG. 6, the articles of Examples 2A and 2B exhibitedthe same or similar average flexural strength using ball-drop height tofailure testing as the strengthened glass substrate of Example 2D,indicating that the articles including a crack mitigating layer retainedtheir respective average flexural strength, while the articles with onlya film (and no crack mitigating layer) (i.e., Example 2C) exhibited asignificant reduction in or lower level average flexural strength.

Examples 3A-3C

Examples 3A-3C are prophetic examples that are illustrated in FIGS. 7-9,with related modeled optical reflectance data shown in FIGS. 10-12.Examples 3A and 3B correlate to Examples 4C and 4E, respectively, whichare discussed below. Example 3A-3C include articles 300, 310, 320 eachincluding a glass substrate 302, 312, 322, a crack mitigating layer 304,314, 324 including polyimide disposed on the glass substrate 302, 312,322 and a film 306, 316, 326 including indium-tin-oxide disposed on theglass substrate 302, 312, 322 such that the crack mitigating layer isbetween the glass substrate and the film. In each of Examples 3A-3C, theglass substrates have a thickness in the range from about 0.2 mm toabout 2.0 mm. Example 3A includes a crack mitigating layer 304 having athickness of 74 nm and a film 306 having a thickness of 115 nm. Example3B includes a crack mitigating layer 314 having a thickness of 85 nm anda film 316 having a thickness of 23 nm. Example 3C includes a crackmitigating layer 324 having a thickness of 64 nm and a film 326 having athickness of 115 nm. Example 3C includes an additional film 328including SiO_(x)N_(y), which functions as a protective layer, disposedbetween the crack mitigating layer 324 and the film 326. The additionalfilm 328 has a thickness of 10 nm. In Examples 3A-3C, the glasssubstrates 302, 312, 322 have a refractive index in the range from about1.45-1.55, the crack mitigating layers 304, 314, 324 have a refractiveindex in the range from about 1.6-1.75 and the films 306, 316, 326 havea refractive index in the range from about 1.8-2.2. In Example 3C, theadditional film 328 including SiOxNy has a refractive index similar tothe refractive index of the crack mitigating layer 324. Each of Examples3A-3C may include a second additional film (illustrated in FIGS. 10, 11and 12) that may include an adhesive, which will be more fully describedin Modeled Example 4.

In each of the articles 300, 310, 320, the thicknesses of the crackmitigating layer and the film were optimized to simultaneously achievegood optical properties and good mechanical properties. The foregoingexamples illustrate that the thickness range of crack mitigating layersand films used in the articles 300, 310, and 320 are effective to retainhigh average flexural strength for the article, while Modeled Examples4C and 4E (described below) illustrate that the articles 300, 310, and320 simultaneously achieve low optical reflectance. Optimization may beachieved by controlling or adjusting one or more process parametersdiscussed with reference to Examples 1A-1J.

Modeled Example 4

Examples 4C and 4E and Comparative Examples 4A, 4B, 4D and 4F wereoptically modeled using the following information in Table 3. Examples4C and 4E correlate to Examples 3A and 3B.

TABLE 3 Refractive index (n, k) values versus wavelength (WL) used inthe optical modeling designs, which are illustrated by FIGS. 10-12.Crack Mitigating Layer Film Glass Substrate Additional Film WL n k WL nk WL n k WL n k 350 1.781 0.000 350 2.28 0.03 300 1.532 0.000 250 1.5780.000 400 1.742 0.000 400 2.2 0.005 450 1.517 0.000 300 1.553 0.000 4501.719 0.000 450 2.15 0.003 550 1.512 0.000 350 1.539 0.000 500 1.7030.000 500 2.11 0.003 700 1.507 0.000 400 1.531 0.000 550 1.693 0.000 5502.07 0.003 1200 1.497 0.000 450 1.525 0.000 600 1.686 0.000 600 2.040.003 0.000 500 1.521 0.000 650 1.680 0.000 650 2.015 0.005 550 1.5190.000 700 1.676 0.000 700 1.995 0.007 600 1.516 0.000 750 1.673 0.000750 1.975 0.01 650 1.515 0.000 850 1.670 0.000 850 1.94 0.02 700 1.5130.000 950 1.668 0.000 950 1.9 0.03 750 1.512 0.000 1150 1.84 0.05 8001.511 0.000 850 1.510 0.000 900 1.509 0.000 950 1.508 0.000 1000 1.5080.000

The articles of Comparative Examples 4A and 4B were modeled using aglass substrate having a thickness of 1.0 mm and are illustrated in FIG.10. In modeled Comparative Example 4A, a film having a thickness of 100nm is disposed on the glass substrate and an additional film disposed onthe film, such that the film is disposed between the glass substrate andthe additional film, as illustrated in FIG. 10. In Comparative Example4B, the model included the additional film being disposed on the glasssubstrate without an intervening film, as also illustrated in FIG. 10.The additional film of Examples 4A and 4B includes an adhesive havingrefractive index of about 1.52. In the optical model, the additionalfilm/adhesive layer was treated as being “very thick”, meaning itrepresents the exit ambient medium in the optical model, where air isthe input ambient medium. This represents a practical case wherereflectance from the distant back surface of the adhesive are notincluded in the model, because this back surface of the adhesive layeris laminated to additional light-absorbing structures such as polarizinglayers, display layers, and device layers that absorb or scattersubstantially all of the light that transmits into the adhesive layer.The adhesive represents one or more of a protective layer, a planarizinglayer, an anti-splinter layer, or an optical bonding layer and otherlayers disclosed herein with reference to the additional film. Asillustrated in FIG. 10, the presence of a high refractive index film,such as indium-tin-oxide, without a properly designed layer structure orcrack mitigating layer, typically causes a significant increase inreflectance in the article, over the visible spectrum.

The articles of Example 4C and Example 4D were modeled using a glasssubstrate having a thickness of 1.0 mm and are illustrated in FIG. 11.In modeled Example 4C, a crack mitigating layer having a thickness of 74nm and including polyimide is disposed on a surface of the glasssubstrate, a film comprising indium-tin-oxide and having a thickness of115 nm is disposed on the crack mitigating layer and an additional filmis disposed on the film. As illustrated in FIG. 11, the crack mitigatinglayer is disposed between the glass substrate and the film, and the filmis disposed between the crack mitigating layer and the additional film.In Example 4D, the modeled article is identical to the modeled articleof Example 4C except no film is included, as illustrated in FIG. 11. Theadditional film of Example 4C and Example 4D includes an adhesive havingrefractive index of about 1.52. The adhesive is also characterized asbeing “very thick”. The adhesive represents one or more of a protectivelayer, a planarizing layer, an anti-splinter layer, or an opticalbonding layer and other layers disclosed herein with reference to theadditional film. Such layers may be commonly used in touch screendevices. As illustrated in FIG. 11, the reflectance of an article withand without a film is similar over a majority of the visible spectrum.Accordingly, when compared to Comparative Example 4A, which showed thepresence of a film significantly increasing the reflectance of anarticle without a crack mitigating layer, the crack mitigating layerabates any increase or variation of reflectance otherwise caused by thepresence of the film. In addition, the article including a glasssubstrate, a film and a crack mitigating layer exhibits a totalreflectance that is substantially similar to, that is, within 5%, 4.5%,4%, 3.5%, 3%, 2.5%, 2%, 1.5% or even 1% of the reflectance of the samearticle without the film (which may still include the crack-mitigatinglayer), across the visible wavelength range such as from about 450 toabout 650 nm, from about 420 nm to about 680 nm or even from about 400nm to about 700 nm.

The total reflectance illustrated in FIG. 11 for both of the articles ofExamples 4C and 4D (i.e., an article with and an article without a film)can be used to demonstrate the contrast between patterned or coatedregions (i.e., regions with a film comprising a transparent conductiveoxide) and non-patterned or uncoated regions (i.e., regions without afilm) in a touch sensor. The touch sensor pattern simulated by Examples4C and 4D (using the refractive index values provided in Table 3) islargely “invisible” due to the less than about 1.5% change in absolutereflectance level between the patterned or coated region (containing thefilm) and the unpatterned or uncoated region (containing no film) in awavelength range from 450-650 nm. The articles of Examples 4C and 4Dalso have a low absolute reflectance level, with total reflectance lessthan about 6% over this same wavelength range. About 4% of the totalreflectance comes from the front (uncoated) glass interface with air andless than 2% of the total reflectance comes from the coated side of theglass substrate (i.e., the crack mitigating layer, film and adhesiveinterfaces).

The articles of Example 4E and Comparative Example 4F were modeled inthe same manner as Example 4C and Comparative Example 4D, respectively;however the crack mitigating layer (comprising polyimide) had athickness of 85 nm and the film (comprising indium-tin-oxide) had athickness of 23 nm. Example 4E included a glass substrate, a crackmitigating layer disposed on the glass substrate, a film disposed on thecrack mitigating layer and an additional film disposed on the film.Comparative Example 4F is identical to Example 4E except it did notinclude the film. As illustrated in FIG. 12, the total reflectance of aglass-film substrate with and without a film is similar over a majorityof the visible spectrum. Accordingly, when compared to ComparativeExample 4A, which showed the presence of a film significantly increasingthe total reflectance of the article without a crack mitigating layer,the presence of a crack mitigating layer abates any increase orvariation of reflectance otherwise caused by the presence of a film. Inother words, an article including a glass substrate, a film and a crackmitigating layer exhibits a total reflectance that is substantiallysimilar to, that is, within 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, oreven 1% of the same article without a film.

Based on Example 3 and modeled Example 4, the articles disclosed hereinmay have a low absolute reflectance and a small change in reflectance(e.g. <1.5%) between regions containing a film and regions notcontaining a film, rendering a patterned touch sensor largely“invisible”, as shown in FIGS. 11 and 12.

Refractive index values for the films and glass substrates used in theoptical modeling of Example 4 were derived from experimental films,optical reflectometry, and estimates known in the literature. It will beapparent to those of ordinary skill in the art that these refractiveindex values can be modified based on material and process choices,requiring a complementary modification to the optimal film thicknessesspecified here. In addition, it will be apparent to those of ordinaryskill in the art that small modifications of the index values in Table 4can be achieved through material and process changes, without departingfrom the spirit of the disclosure. Likewise, small changes in the filmand substrate thicknesses and design can be utilized without departingfrom the spirit of the disclosure. Further, the crack mitigating layersin Example 3 and modeled Example 4 can be chosen to comprise additionalmaterials having similar refractive indices, and in some cases may notinclude polyimide. For example, the crack mitigating layers in Examples3 and 4 may comprise nanoporous inorganic layers, alternative polymermaterials, or other materials mentioned elsewhere herein.

While the disclosure has been described with respect to a limited numberof embodiments for the purpose of illustration, those skilled in theart, having benefit of this disclosure, will appreciate that otherembodiments can be devised which do not depart from the scope of thedisclosure as disclosed herein. Accordingly, various modifications,adaptations and alternatives may occur to one skilled in the art withoutdeparting from the spirit and scope of the present disclosure.

We claim:
 1. An article, comprising: a substrate having a thickness andopposing major surfaces including a first major surface and a secondmajor surface; a crack mitigating layer disposed on and directly incontact with the first major surface of the substrate, wherein the crackmitigating layer comprises a porous or non-porous polymeric or hybridorganic-inorganic material and has a thickness from about 0.01 μm toabout 10 μm; and a first film disposed on the crack mitigating layerhaving a thickness from about 0.01 μm to about 20 μm, wherein an averagestrain-to-failure of the substrate is 0.5% or greater, as measured withthe crack mitigating layer disposed on and directly in contact with thefirst major surface of the substrate and the first film disposed on thecrack mitigating layer.
 2. The article according to claim 1, wherein thecrack mitigating layer has a modulus that is less than a modulus of thefirst film and a modulus of the substrate.
 3. The article according toclaim 1, wherein the substrate is a glass substrate that is chemicallystrengthened and has a surface compressive stress of at least 500 MPaand a compressive depth of layer of at least 15 μm.
 4. The articleaccording to claim 1, wherein the crack mitigating layer prevents cracksoriginating in one of the first film and the substrate from bridging tothe other of the first film and the substrate.
 5. The article accordingto claim 1, wherein the first film further comprises one or more of anaverage strain-to-failure that is less than an average strain-to-failureof the substrate and a modulus that is greater than a modulus of thesubstrate, and wherein the first film is a layered structure.
 6. Thearticle according to claim 5, wherein the first film comprises ananti-reflection (AR) film.
 7. The article according to claim 1, whereinthe crack mitigating layer comprises a silicon-containing material. 8.The article according to claim 1, wherein the article exhibits areflectance of about 10% or less across a visible wavelength range from400 nm to 700 nm.
 9. A display device comprising the article of claim 1,wherein the article serves as a protective cover for the display device.10. An article, comprising: a substrate having a thickness and opposingmajor surfaces including a first major surface and a second majorsurface; a crack mitigating layer disposed on and directly in contactwith the first major surface of the substrate, wherein the crackmitigating layer comprises a porous or non-porous polymeric or hybridorganic-inorganic material; a first film disposed on the crackmitigating layer having a thickness from about 0.01 μm to about 20 μm;and a further film disposed on the second major surface of the substratehaving a thickness from about 0.01 μm to about 20 μm, wherein an averagestrain-to-failure of the substrate is 0.5% or greater, as measured withthe crack mitigating layer disposed on and directly in contact with thefirst major surface of the substrate and the first film disposed on thecrack mitigating layer.
 11. The article according to claim 10, whereinthe further film is a layered structure, and further wherein the furtherfilm comprises a scratch-resistant layer.
 12. The article according toclaim 10, wherein the further film comprises one or more of SiO₂, Si₃N₄,SiO_(x)N_(y), and combinations thereof.
 13. The article according toclaim 10, wherein the article further comprises: one or more additionalfilms disposed on the second major surface of the substrate comprisingone or more of SiO_(x), SiN_(y), SiO_(x)N_(y), and combinations thereof.14. The article according to claim 10, wherein the first film comprisesan anti-reflection (AR) film.
 15. The article according to claim 14,wherein the first film further comprises a fingerprint-resistant layer.16. The article according to claim 14, wherein the AR film is a layeredstructure comprising one or more of SiO₂, TiO₂ and Nb₂O₅.
 17. Thearticle according to claim 10, wherein the crack mitigating layer has athickness from about 0.01 μm to about 10 μm.
 18. The article accordingto claim 10, wherein the crack mitigating layer has a thickness fromabout 0.01 μm to about 0.5 μm.
 19. The article according to claim 10,wherein the crack mitigating layer has a modulus that is less than amodulus of the first film and a modulus of the substrate.
 20. Thearticle according to claim 10, wherein the substrate is a glasssubstrate that is chemically strengthened and has a surface compressivestress of at least 500 MPa and a compressive depth of layer of at least15 μm.
 21. The article according to claim 10, wherein the first filmfurther comprises one or more of an average strain-to-failure that isless than an average strain-to-failure of the substrate and a modulusthat is greater than a modulus of the substrate.
 22. The articleaccording to claim 10, wherein the crack mitigating layer comprises asilicon-containing material.
 23. The article according to claim 10,wherein the article exhibits a reflectance of about 10% or less across avisible wavelength range from 400 nm to 700 nm.
 24. A display devicecomprising the article of claim 10, wherein the article serves as aprotective cover for the display device.
 25. An article, comprising: aglass substrate having a thickness and opposing major surfaces includinga first major surface and a second major surface; a crack mitigatinglayer disposed on and directly in contact with the first major surfaceof the glass substrate, wherein the crack mitigating layer comprises apolymeric material and has a thickness from about 0.01 μm to about 0.25μm; a first film disposed on the crack mitigating layer having athickness from about 0.01 μm to about 20 μm; and a further film disposedon the second major surface of the substrate having a thickness fromabout 0.01 μm to about 20 μm, wherein an average strain-to-failure ofthe glass substrate is 0.5% or greater, as measured with the crackmitigating layer disposed on and directly in contact with the firstmajor surface of the substrate and the first film disposed on the crackmitigating layer, wherein the first film comprises one or more of SiO₂,Al₂O₃, Nb₂O₅, Ta₂O₅, TiO₂, and combinations thereof, wherein the furtherfilm is a layered structure that comprises a scratch-resistant layer andone or more of SiO₂, SiO_(x), SiN_(y), Si₃N₄, SiO_(x)N_(y), andcombinations thereof, and further wherein the substrate is chemicallystrengthened and has a surface compressive stress of at least 500 MPaand a compressive depth of layer of at least 15 μm.
 26. The articleaccording to claim 25, wherein the crack mitigating layer furthercomprises a modulus that is less than a modulus of the first film and amodulus of the substrate.
 27. The article according to claim 25, whereinthe crack mitigating layer comprises a fracture toughness of 0.5MPa*m^(1/2) or greater.
 28. The article according to claim 25, whereinthe first film further comprises a modulus of at least 25 GPa and ahardness of at least 1.75 GPa.
 29. The article according to claim 25,wherein the article exhibits a reflectance of about 10% or less across avisible wavelength range from 400 nm to 700 nm.
 30. The articleaccording to claim 25, wherein the first film comprises a layeredanti-reflection (AR) film comprising one or more of SiO₂, TiO₂ andNb₂O₅.